ZestyThanks.
For the things where you're making numeric changes to font/ element sizes, is there some formula you're using for this or is it entirely trial and error? I don't see any documentation about how the UI scaling is actually implemented and I'd like for everything to be the same size and in the same location as it was before without having to spend hours testing values.
An update on this. The issue was caused by my health and ammo using the "TF2 Build" font for my HudFontHUGE in my edited version of PVHud. I had to edit the "tall" value of this font in ClientScheme.res from 80 to 56 for it to display consistently to the way it previously did on 1080p. To work this out I had to go in and test values in ClientScheme.res and manually compare the pixels in two screenshots in photoshop each time and 80 -> 56 gives an exact match. Not sure why 1080p requires a 70% scaling to match previous behaviour but thought it might be useful for other people with broken hud elements.