No, you'd be pushing them on the way up for their double-jump, and if they're doing it low enough where they still won't get touched, then you should be able to jump around them/grab the ledge before them (in theory, anyway; we all know it doesn't really work like that).are you sure that water gun can hit someone under the stage?
But, Water Gun can hit slightly under the lip; I think that's enough to prevent a ledge fall -> double-jump from being able to grab the edge.