You can place the player start at the same location as your player, and just scale it to have the same proportions as your player. Then it’s going to work.
The reason why it’s not really worth the worry, is that the character placement is approximate anyway. Haven’t you ever noticed that ‘drop’ as your character sort of falls into the level? So as long as you put the start in roughly the right place, you’ll be fine.
You’re right about not missing something important. From my work with the engine so far ( and probably any other package this complex ) is, don’t get hung up on stuff. Just find a way forward. If you want a hermetically sealed ‘super solution’ to everything, you will always be hitting brick walls, and will not get to where you want to go 