The game's resolution is scaled to whatever your monitor currently uses. There's an option to disable the UI Scaling under Options > Graphics, called "Scale User Interface". Is that what you're looking for?
Until I put a mod on my UI, I had a similar problem - scaled was blurry, and at res (5k monitor) was nasty small (I could fit the whole area map into my view, which was cool however). For awhile I was forcing my computer to drop resolution via system settings to not have to scale UI. The mod that I used can be found in the 'UI Modding' forum category - its pretty nifty and seems to have nixed this problem (it also might be switching to the Beamdog version of BGEE/SoD which behaves somewhat differently than my prior Steam version).
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Good luck!