I agree – slide over apps should have all of the same size options. Limiting to 1/3 makes them feel much too cramped with tons of unused screen real estate.I wish this was more of a hot corner - launch a specified app I choose in slide over - rather than only being notes. Let slide over have the same size options as standard apps (1/3, 1/2,2/3) and that would be perfect.
Edit: I really dislike random 1-off UI systems that only apple gets to use when a general system would be just as good.