Let’s say you, a Medium character, are in a 5ft wide, 10ft tall corridor, and that a Medium enemy creature stands in your way. You wish to go behind the enemy creature using your fly speed (either disengaging, or just not particularly caring about getting an opportunity attack).
Considering that you cannot go through an enemy creature’s controlled space (unless said creature is two size categories above you), but that Medium creatures control a space of 5ft on a side, can a Medium creature fly over an enemy Medium creature in a 10ft high corridor ?
The reason I’m asking is because in a game I played (where I was the flying character), the DM claimed that creatures control a bigger space vertically (10ft instead of 5ft, or 2 squares instead of 1), and therefore flying over the enemy in this case is impossible. I don’t recall any place in the PHB/DMG/XGR where vertical controlled space is to be bigger than what the size category says, but the DM seemed convinced he was correct. Maybe I’m missing something ?
Relevant rules :
you can move through a hostile creature's space only if the creature is at least two sizes larger or smaller than you
Each creature takes up a different amount of space. The Size Categories table show s how much space a creature o f a particular size controls in combat.
Medium 5 by 5 ft
A creature's space is the area in feet that it effectively controls in combat, not an expression of its physical dimensions. A typical Medium creature isn't 5 feet wide, for example, but it does control a space that wide.