You can't shoot down over waist high obstacles full stop. The projectiles of anything other than magic missile are drawn from the centre of the character's body roughly belly button height on a tall human/elf/tiefling. Yet the animation has the projectile leave their hands when magic or the held bow/crossbow if arrow. It makes no sense and discourages interesting strategic play as iirc enemy characters can shoot through bannisters.
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https://imgur.com/BlUFjlg[/img]
Note the in the image my oathbreaker paladin (selected) is trying to cast eldritch blast to the banite through the doorway, the projectile ghost is starting from his bellybutton and stops at the bannister yet the projectile will be fire from his hands. Unless blind firing, any projectile will always be shot from around eye level or at least inline with the eye to target.
I have tried to play tactically by putting my group on a balcony and using hunger of hadar to slow/funnel them through another doorway. This issue is consistent across all acts and areas of the game where scenery that is waist high to a medium character cannot be shot over.
