Recommendation ITU-R BT.1729 test image for 5:4 display
The recommendation doesn't specify what to with this lower aspect ratio.


And yet it is perfectly clear about the purpose and design of each of the zones. Why can't you simply adjust the size and/or arrangement of the zones to meet your needs? They even give an example of how to do that for 4:3.

But if all you're doing is verifying the performance of a flat-panel display attached to the end of a digital RGB signal chain, then the tests performed in many of the zones are simply irrelevant to you.