Thats right, this year it seems that signing counts towards the 4K so there isn't much signing going on since it means you can fit less game in.
Kev
I thought signing did NOT count towards the 4k if an unsigned version is also provided that is within 4k?
With respect to the original problem...
There is probably an API somewhere that you should be using to find the overhead of the title bar and other things and adjust your frame size accordingly... this same problem applies if you have changed the title bar font to a larger font for example.