I am more a programmer and a lazy one: spoiled by navMesh how works fine for the most of the cases and not for what you suggest in the beginning - it did not work with 89° for both.
I am afraid have to make it the hard way with possibilities of many errors.
All could be avoided if a feature (think existed in the past) to add custom geometry to be used for navigation, because the one I made for collision with 89° works fine.