Per the 5e rules the DM is free to award advantage for any situation that they deem appropriate. Our DM, Larian, gives advantage for being behind a target(and attacking from high ground).
A multi-million dollar company should be able to craft a better turn based combat game than a pretty "attack from behind jump to high ground" romp. Especially since they have well balanced source material that already plays really well.
It's pretty amazing how badly BG3 combat plays, really. It seems like they're so blindly stuck on "misses are bad" and "resting restrictions are bad" that they can't see how the gameplay suffers much more from their changes. Maybe everything is not ideal for whatever "works in a modern videogame", but in this case it's just better to stick with the system you have and make the most of it, rather than make it a worse hybrid version of two different systems.
