why can't I use "en haut de" for "on top of"? When I look up the phrase "au-dessus" means "above" so I'm very confused between the meaning and usage

Hi James,

I think that it is the nuance between "at the top of  -- summit"  en haut de     versus "above" au-dessus.

https://www.wordreference.com/fren/au-dessus?s=%C3%AAtre%20au-dessus%20de

Have a look at the link.

Jim