Vertical alignment with array package when the line width is fixed

Question

I created a post earlier on the same topic (Vertical alignment in tables). I got an answer but it triggered another question.

Below the solution that has been provided. I would expect vertical centering but the text goes on top of each cell. Playing with p, m, and b to align vertically doesn't seem to work here. I have probably missed something...

\documentclass{article}
\usepackage[english]{babel}
\usepackage{array}

\begin{document}

\begin{tabular}{ |m{2cm}|m{2cm}|m{2cm}|@{}l@{}}
   \hline
     x &
     x &
     x &\\[5mm]
   \hline
\end{tabular}

\end{document}

Answer 1

As seen in the second row, the m column type is giving vertical centering of the cells, however the extra space from \\[..] is added afterwards so if your entries are only one line b and p are the same thing (and m isn't very different). As I noted in a comment on the previous answer, because m cells typically have large depth, you typically need to use a large value in the optional argument of \\[] before increasing the depth of the strut makes any difference. Or better try to avoid using the optional argument of \\ in tables.