I am planning an encounter with Giant Wasps within a hallway with 15 foot ceilings. I think RAW, a Medium character would be in the first 5 feet from the floor and only threaten the middle 5 ft square, but many Medium characters are technically taller than 5 feet.
If a wasp flies along the ceiling, would it avoid any opportunity attacks from the characters on the floor?
You can make an opportunity attack when a hostile creature that you can see moves out of your reach.
Opportunity attacks only occur if you go from being within somebody's reach to being outside it, if their reach is 5 feet and you remain 10 feet away, you will not provoke opportunity attacks.
Most creatures have a 5-foot reach and can thus attack targets within 5 feet of them when making a melee attack.
Medium creatures effectively control a 15×15×15 region (with the creature effectively occupying the center 5×5×5 cube) regardless of their actual height. Thus, if a creature is two squares above them, that creature is 10 feet away and already out of their reach (various features and Reach weapons aside). In other words, the wasp would avoid any and all opportunity attacks because it is never in a region that the Medium creature can reach.
