How to apply transition on foreground image only ?

Hello

I'm creating video where I have a background video and I show images over it (kind of animated slideshow)

My goal is to create simple "drop in" transitions between images.

I've downloaded this package: https://elements.envato.com/minimal-transitons-for-fcpx-TGHHXKN

The problem is that when I apply my transition on foreground image, the transition apply on both foreground and background. So I have a foreground + backgroung droppin in on the background, and it don't look good. I only want the foreground image to drop in

I'm using scale (at 50%) to resize the image.

Also tried with some native transitions and I have the same problems

Any tips for fixing that ?

Thanks

Version: 10.6.5