What was I thinking doubting you?
Of course you got the things right using the display resolution and not the video height! I’ve used :
<refresh resolution="2160">
<min>23</min>
<rate>23.976</rate>
<max>24</max>
<delay>250</delay>
</refresh>
and I get the same good results as before using the “old” format you added in nightly 20241129.
I managed to get my hands on a UHD video with dialogs and size 3840x1600 as top/bottom bars were cropped and of course, it played perfectly as expected!