How to make a mask effect affect :-) only the video track for which it was created?

[Vájet Törp]

Hello,
for example:
I create a shadow effect by a block color with a large soft edge on a petal drawing. Other petals of the flower are placed on lower video tracks, and they have their "own" shadows too, but they are also covered by this shadow (soft edge) on the upper track already. The result is too much and shapeless darkness...