ES Theme beginner question - maxSize?

[wawa]

Hoping someone here could help me out with what seems like a trivial problem - I don't think I properly understand maxSize. I checked the documentation from https://github.com/RetroPie/EmulationStation/blob/master/THEMES.md, which says:

maxSize - type: NORMALIZED_PAIR.
The image will be resized as large as possible so that it fits within this size and maintains its aspect ratio. Use this instead of size when you don't know what kind of image you're using so it doesn't get grossly oversized on one axis (e.g. with a game's image metadata).

But when I try entering this in my theme XML, the image does not maintain it's aspect ratio, and seems to work identically to when I just use size ...

So I went back to the docs, and noticed this:

size - type: NORMALIZED_PAIR.
If only one axis is specified (and the other is zero), the other will be automatically calculated in accordance with the image's aspect ratio.

Instead, I tried using <size> 1 0 </size>, hoping that only specifying one axis would solve my issue - but I got the same result.

The only time I can get the image to respect aspect ratio seems to be if I use tile, which I don't want to do in this case.

For some context, I'm using a pi4b with the latest version of retropie, and I'm using an unconventional display - a 270x270 square display. The image seems to display correctly when I run ES it on windows at the same resolution - are there differences in how the XML is interpreted on the pi, and if so, is it documented somewhere?