Advantages do NOT stack. They cancel with Disadvantage for a net neutral roll (though I believe in BG3's implementation, 2 Advantages + 1 Disadvantage = net Advantage). However, in the absence of Disadvantage, 2 (or 1000) sources of Advantages is mechanically the same as a single source of Advantage. BG3's decision to calculate the difference in # of Advantages and Disadvantages (iirc) is the only saving grace for Height Advantage. If you want height bonus to stack with other sources, it'd be better as a +2 bonus to your attack roll. Then this would always stack with sources of Advantage.
Originally Posted by lofgren
2. Yes, getting height is a core aspect of combat. We don't have any disagreement on this point. 3. I am skeptical that ranged attacks from high ground constitute such a huge percentage of rolls, even attack rolls, that all other rolls are "few and far between." This sounds like a personal playstyle quirk, not a fact of the game.
These points are contradictory, unless you're defining "huge percentage of rolls" as >50% of the total combat rolls. Which is way too strict of a criteria. Height needs to be present for only ~20% of rolls to be a significant gameplay factor, especially because those 20% of rolls will be rolled by only your 1 or 2 ranged party members. Meaning that for those characters, ~50+% of their attacks will be high ground attacks. Which is a lot. Larian has clearly developed BG3 so that height is present in almost every encounter, so 20% of rolls is probably an underestimate if anything. Don't forget, you also have to take into account the rolls where you get disadvantage from low ground.
Personally, I'd rather have to use characters' abilities to gain bonuses as powerful as Advantage. The great thing about D&D parties is the fact that they're a team and can work together to be greater than the sum of individuals. The basically ~free high ground Advantage in many cases overshadows this potential synergy.