I have a character using the Spider Climb spell and a whip in a dungeon with 20 foot ceilings. Character is 6 foot tall. Average Medium sized creature is 4+ feet tall. Average Human 5'9". If PC is on the ceiling what is the range they can attack into?
If PC threatens 5 foot base square on ceiling + 5 foot standard reach + 5 foot extra reach from whip, that is makes 15 feet total. From a 20 foot ceiling, would that mean any Medium creature over 5 feet is within the 15 foot reach? Any creature over 5 feet would extend into the square threatened by the 15 foot reach. Or is any Medium sized creature only considered to occupy 5 feet square no matter how much taller they are.
I think it is slightly different than asking how much reach a creature has. It is more of a question about how many squares a creature is vulnerable and can be attacked into. The question is there are two different numbers given for "Medium" creatures. I realize 5 foot square is mainly to determine horizontal ranges, but it also clearly states medium creatures can be over 5 feet in height. Probably the majority are.
I realize one can say an enemy can just duck down. But maneuvering to avoid an attack is usually thought to be already included in fighting mechanics. As normal characters don't occupy the entire 5 foot width or depth of a horizontal square and can move around to avoid attacks.
Also, I realize this might be over scrutinizing things, but there really are two separate numbers given for medium creatures: 5 foot square (horizontally), and 4-9 foot height vertically. Is there any guide given to 3D or vertical workings?