So your PlayerBox sprite is 32x32px.
Create a new sprite, size 50x100, name it PlayerFallingBox. Add Pin behavior. Make it invisible.
On start of layout set its position to PlayerBox and pin it to PlayerBox.
Change your event to something like this:
PlayerFallingBox on collision with Enemy
(and) PlayerBox is Falling
(and) PlayerBox.y<Enemy.y -> Subtract 1 from Health
So this bigger PlayerFallingBox sprite will only be used to detect collisions when the player is falling.
In all other events continue to use PlayerBox.