In Bannerlord, any position that allows the defenders to send arrows down allows the attackers to send arrows up, and it isn't an equal relationship since -- as far as the game is concerned -- any wall at upper-chest level will block the arrow of the person behind the wall, but still allow them to be headshot. People call it cheese, but it is using almost-literal textbook assault tactics and the current AI can't cope because its imperative to hold the wall at all costs.
But that's silly. The wall is an advantage precisely because it can be (not must!) be used to deny the enemy ranged units the ability to tear into packed-rank formations below, along with channelizing the along predictable and very limited routes (towers, stairs). If the defenders are to cede the wall, they shouldn't just mill around aimlessly but reverse the situation by massing their own archers to cover it as attackers filter in, essentially reversing the situation, still forcing attackers to endure an arrow storm -- but on their own terms.
There are Bannerlord castles where it is already in effect, with the archers having not just the wall but an interior fallback position where they can cover the wall in arrows and the attackers can't mass against them effectively. But all of them should work that way, because that was the way real castle defenses functioned*.
(*With the caveat that you're going to find about a million and one exceptions if you look at historical examples. Some castles had front-loaded defense, others were simply poorly engineered because they were more of a rich *******'s house than an actual fortification.)
edit:
It is hard to tell (arrows break when hitting stone now) but they seem to be a lot better about it, but that's because they won't loose with an obstruction in the way. It still happens occasionally, but not that often, as far as I can tell.