best way might be to find all the players in the explosion, and then fire raycasts to each corner of their collision box and the middle, if any of them reach, do stuff to them
there might be small problems where you could have each area blocked, with a hole to the top of the head or something, but it's less error than just having one raycast to the middle of the player
That's what I was thinking
You can do it with math too, dunno if it's faster engine-wise
Poll