Running the game at 2560x1440 makes the UI pretty small, so I'm using a GUI scaling factor of 2.0.
This works really well for a majority of the UI, however the icons for spell effects aren't scaled along with everything else. I'm using the I Heart Vanilla modlist, and can confirm that Big Icons is functioning correctly as I can see a noticeable improvement in the quality of spell icons.
I noticed people in the comments of Big Icons are having similar issues with various builds of OpenMW, so I figured I'd see if anyone here has come across a solution or has a working example. Maybe unrelated, but the HUD local map also doesn't increase in size when changing local map hud widget size.