If you want a fixed other size it is very easy to change. Check out live_game.css in PA/media/ui/alpha/live_game/ there is a class called "pip".
Btw; I got the same result as you when trying to add additional PIP screens - only the icons rendered.
Meh. I have no idea what triggers the filling with textures. Somehow I feel it's coherent magic that we have no influence on.
We've been working on other hacks like draggable (Currently working, mod is on PAMM) and multi-monitor (Hacky, but works). Resize is the next step after that!
Yes it sure is. https://forums.uberent.com/threads/rel-draggable-picture-in-picture.56738/#post-877273