The prone condition specifies advantage on attacks within 5 feet of the prone target, so a melee attack with a reach weapon made at 10 feet would be at disadvantage, while an attack with a ranged weapon made next to the target is a straight roll, yes? Thnx!
— Infright Heck (@insightcheckpod) October 14, 2018
If the D&D rules refer to an attack made within 5 feet of a target, it means exactly that: an attack within 5 feet.
If the rules require an attack to be a melee or a ranged attack, the rules say so.
— Jeremy Crawford (@JeremyECrawford) October 15, 2018