Yes the DPI setting is only for Windows itself, not setup/WinPE.
If you know the size of a US quarter, then you can see how a UEFI only tablet looks like with the Gimagex HTA that I have in my signature:
While the text specified by the HTA scaled "appropriately" I can tell you that must custom imaging GUI (which is not shown) is super tiny. As long as this remains to be true, I will eventually have to learn how to program my GUI to scale as well. So I feel your pain.