Align top of images using subcaption

Question

I'm trying to align the tops of two images using the subfigure environment from the subcaption package. Unless I'm misinterpreting the other questions, I believe I have read multiple questions asking the same, Align by the top borders of figures when using subcaption and How to prevent offset in subcaption / subfigure are two examples. The problem is, those answers don't seem to work as I expected, and I still can't get the tops of the images to be aligned.

example:

\documentclass{article}
\usepackage{subcaption}
\usepackage{graphicx}
\usepackage{mwe}
\begin{document}
    \begin{figure}
        \centering
        \begin{subfigure}[t]{0.45\textwidth}
            \includegraphics[width=\linewidth, height=20em]{example-image-a}
            \caption{taller image}
        \end{subfigure}
        \begin{subfigure}[t]{0.45\textwidth}
            \includegraphics[width=\linewidth, height=15em]{example-image-b}
            \caption{shorter image}
        \end{subfigure}
        \caption{two images}
    \end{figure}
\end{document}

For me this generates the following:

I would have expected it to align the tops of the images. How do I do this?

Answer 1

The problem is that [t] aligns to the first baseline ([b] to the last baseline) of the included paragraph, not the top of the content. The baseline of images lies on there lower edge, so [t] has basically no effect with two images. Lower the images to include the baseline on top or add an empty line above them (using e.g. \vskip 0pt) to make it work.

Further information on this problem can be found in Understanding minipages - aligning at top. Note that subfigure uses a minipage (or the equivialent?) internally.