I think your idea is an elegant compromise and solution to implement SS. The more I read the forums and the more I played the game, I realized how hard it actually is to get penalties in BG3. Almost everything is in your favor. At least your method provides an added reason to select SS beyond the -5/+10 portion of the feat. I also wouldn't raise the AC bonus past +2. More than that, high ground becomes effectively too important to give up and we're back to the same problem we have now.
Hmm, you're right about that. There are really no penalties at the moment besides trying to shoot at things beyond a certain attack range, and ranged characters being too close to an enemy, but it's also noticeable that threaten range is way too large for whatever reason. (Perhaps the extreme threaten range is supposed to be a poor compromise for the high ground advantage system? But that's yet another supporting theory for how that particular mechanic is basically the main factor behind most of the other design decisions.)
To be fair, there are hardly any penalties in tabletop DnD either. We just don't see the majority of things that impose disadvantage in BG3 because there's no bright light/dim light/unlit system in regards to accuracy (and there probably shouldn't be, because that's another balancing nightmare in itself), and we haven't run into any enemies using spells like Darkness or anything that blinds us yet.
