Not saying you should just wondering if you are since otherwise it should work I think. For example does this basic playground from the GUI doc work on the mobile devices that you’re testing on? It sets the control’s width and height in pixels and has no other size or scaling configuration and it isn’t hosed on my iPhone for example. So I wonder what you’re doing differently if that one works for you.
Well I’ve gotten a few working about how I wanted but am by no means an expert on BJS GUI’s for mobile. Maybe others will be able to help more but I imagine will be difficult without a small reproduction. If it happens with a simple rectangle set in pixels like you said then it seems that could be reproduced in a small playground? 