Allineamento di tkzpicture in ambiente tabular

Un esempio minimo compilabile è il seguente
`\documentclass[a4paper,11pt]{article}

\usepackage{xcolor}
\usepackage[utf8]{inputenc}
\usepackage{amsmath,amsfonts,amssymb}
\usepackage{bm}
\usepackage[super]{nth}
\usepackage{calc}
\usepackage{tikz}
%\usepackage{pbox}
\usetikzlibrary{decorations}
\usetikzlibrary{calc}
\usetikzlibrary{patterns}
\usetikzlibrary{shapes.arrows}
\usepackage{tikzscale}
\usepackage{pgfplots}
\usepackage{tabularx}
\pgfplotsset{compat=1.12}
\usepackage[font=small, format=hang, labelfont={sf,bf}, tableposition=top, figureposition=bottom]{caption}

\begin{document}

\begin{figure}
\centering
\begin{tabular}{lr}
%\tikzsetnextfilename{re1}
\includegraphics{immagini/tikz/wpvsw/re1.tikz}
&
%\tikzsetnextfilename{im1}
\includegraphics{immagini/tikz/wpvsw/im1.tikz}
\\
%\tikzsetnextfilename{re2}
\includegraphics{immagini/tikz/wpvsw/re2.tikz}
&
%\tikzsetnextfilename{im2}
\includegraphics{immagini/tikz/wpvsw/im2.tikz}
\\
%\tikzsetnextfilename{re3}
\includegraphics{immagini/tikz/wpvsw/re3.tikz}
&
%\tikzsetnextfilename{im3}
\includegraphics{immagini/tikz/wpvsw/im3.tikz}
\\
\end{tabular}%
\caption{\textsl{Left}: Plot of the real part of the modified wavenumber, $w'_\text{r}$, vs. wavenumber $w$ for first derivative approximations: (a) \nth{2} order explicit; (b) \nth{4} order explicit.}
\end{figure}
\end{document}`

che si poggia sui file seguenti (upper-left, middle-left, lower-left, upper-right, middle-right, lower-right), messi assieme seguendo l’esempio della guida di tikz
`\begin{tikzpicture}[baseline,trim axis left]
\tikzset{every mark/.append style={scale=.75,fill=white}}
\pgfplotsset{every tick label/.append style={
/pgf/number format/precision=1,
/pgf/number format/fixed,
/pgf/number format/fixed zerofill
}}
\pgfplotsset{every axis plot/.append style={line width=.25pt}}

\begin{axis}[width=.5\textwidth,height=.5\textwidth,
ylabel={$\text{Re}\left(k'\right)$},
xmin=0,xmax=pi,ymin=0,ymax=pi,axis equal image=true,
xtick={.5,1,…,3},
xticklabels={},
ytick={.5,1,…,3},
grid=major]%,trim axis left]
\addplot[mark=none] {x};
\end{axis}

\draw[red]
(current axis.below south west)
rectangle (current axis.above north east);
\draw[red]
(current axis.left of south west)
rectangle (current axis.right of north east);

\end{tikzpicture}
`

`\begin{tikzpicture}[baseline,trim axis left]
\tikzset{every mark/.append style={scale=.75,fill=white}}
\pgfplotsset{every tick label/.append style={
/pgf/number format/precision=1,
/pgf/number format/fixed,
/pgf/number format/fixed zerofill
}}
\pgfplotsset{every axis plot/.append style={line width=.25pt}}

\begin{axis}[width=.5\textwidth,height=.5\textwidth,
xmin=0,xmax=pi,ymin=0,ymax=pi,axis equal image=true,
xtick={.5,1,…,3},
xticklabels={},
ylabel={$\text{Re}\left(k'\right)$},
ytick={.5,1,…,3},
grid=major]%,trim axis left]
\addplot[mark=none] {x};
\end{axis}

\draw[red]
(current axis.below south west)
rectangle (current axis.above north east);
\draw[red]
(current axis.left of south west)
rectangle (current axis.right of north east);

\end{tikzpicture}
`

`\begin{tikzpicture}[baseline,trim axis left]
\tikzset{every mark/.append style={scale=.75,fill=white}}
\pgfplotsset{every tick label/.append style={
/pgf/number format/precision=1,
/pgf/number format/fixed,
/pgf/number format/fixed zerofill
}}
\pgfplotsset{every axis plot/.append style={line width=.25pt}}

\begin{axis}[width=.5\textwidth,height=.5\textwidth,
xlabel={$k$},
xmin=0,xmax=pi,ymin=0,ymax=pi,axis equal image=true,
xtick={.5,1,…,3},
%xticklabels={},
ylabel={$\text{Re}\left(k'\right)$},
ytick={.5,1,…,3},
grid=major]%,trim axis left]
\addplot[mark=none] {x};
\end{axis}

\draw[red]
(current axis.below south west)
rectangle (current axis.above north east);
\draw[red]
(current axis.left of south west)
rectangle (current axis.right of north east);

\end{tikzpicture}
`

`\begin{tikzpicture}[baseline,trim axis right]
\tikzset{every mark/.append style={scale=.75,fill=white}}
\pgfplotsset{every tick label/.append style={
/pgf/number format/precision=1,
/pgf/number format/fixed,
/pgf/number format/fixed zerofill
}}
\pgfplotsset{every axis plot/.append style={line width=.25pt}}

\begin{axis}[width=.5\textwidth,height=.5\textwidth,
ylabel={$\text{Im}\left(k'\right)$},
xmin=0,xmax=pi,ymin=-2e-2,ymax=1.6e-1,
xtick={.5,1,…,3},
xticklabels={},
ytick={0,2e-2,4e-2,6e-2,8e-2,10e-2,12e-2,14e-2,16e-2},
scaled y ticks={base 10:2},tick scale binop=\times,
yticklabel pos=right,
grid=major]%,trim axis right]
\end{axis}

\draw[red]
(current axis.below south west)
rectangle (current axis.above north east);
\draw[red]
(current axis.left of south west)
rectangle (current axis.right of north east);

\end{tikzpicture}`

`\begin{tikzpicture}[baseline,trim axis right]
\tikzset{every mark/.append style={scale=.75,fill=white}}
\pgfplotsset{every tick label/.append style={
/pgf/number format/precision=1,
/pgf/number format/fixed,
/pgf/number format/fixed zerofill
}}
\pgfplotsset{every axis plot/.append style={line width=.25pt}}

\begin{axis}[width=.5\textwidth,height=.5\textwidth,
xticklabels={},ylabel={$\text{Im}\left(k'\right)$},
xmin=0,xmax=pi,ymin=-2e-2,ymax=1.6e-1,
xtick={.5,1,…,3},
ytick={0,2e-2,4e-2,6e-2,8e-2,10e-2,12e-2,14e-2,16e-2},
scaled y ticks={base 10:2},tick scale binop=\times,
yticklabel pos=right,
grid=major]%,trim axis right]
\end{axis}

\draw[red]
(current axis.below south west)
rectangle (current axis.above north east);
\draw[red]
(current axis.left of south west)
rectangle (current axis.right of north east);
\end{tikzpicture}`

`\begin{tikzpicture}[baseline,trim axis right]
\tikzset{every mark/.append style={scale=.75,fill=white}}
\pgfplotsset{every tick label/.append style={
/pgf/number format/precision=1,
/pgf/number format/fixed,
/pgf/number format/fixed zerofill
}}
\pgfplotsset{every axis plot/.append style={line width=.25pt}}

\begin{axis}[width=.5\textwidth,height=.5\textwidth,
xlabel={$k$},ylabel={$\text{Im}\left(k'\right)$},
xmin=0,xmax=pi,ymin=-2e-2,ymax=1.6e-1,
xtick={.5,1,…,3},
ytick={0,2e-2,4e-2,6e-2,8e-2,10e-2,12e-2,14e-2,16e-2},
scaled y ticks={base 10:2},tick scale binop=\times,
yticklabel pos=right,
grid=major]%,trim axis right]
\end{axis}

\draw[red]
(current axis.below south west)
rectangle (current axis.above north east);
\draw[red]
(current axis.left of south west)
rectangle (current axis.right of north east);

\end{tikzpicture}`

Come potete vedere ho usato trim axis left (e right) come opzione di tikzpicture, ottenendo il primo file allegato (cattura2). Ho postato la domanda anche su tex.stackexchange, e un consiglio è stato di usare trim axis left (e right) come opzione dell’ambiente axis. Ho provato, ma il risultato è quello del secondo file allegato (cattura).

Grazie per l’attenzione,
Enrico Maria

EDIT: in entrambi i casi l’allineamento relativo tra le varie tele mi sembra perfetto, il fatto è che non occupano esattamente la \textwidth (o ne occupano di meno, o di più).
Casomai ci si chiedesse perché imposto width ed height nelle opzioni di \begin{axis} anziché in quelle di \includegraphics, la risposta è che è l’unico modo che ho trovato di far uscire delle tele quadrata anche per assi x e y con scale ad ordini di grandezza diverse (quelle a destra)