I wouldn't mix platform- and physic-behavior. That can cause bad side effects.
The physic-behavior has 'VelocityY' what you can use.
+ Player: Is overlapping Ground at offset (0, 20)
+ System: Trigger once
-> System: Set impactSpeed to Player.Physics.VelocityY
It's not so elegant, but it works. The problem is the elasticity of your falling object. It jumps several times when it hits the ground.
You have to tweak the offset of the overlapping. It depends on the elasticity and the size of the falling object.