Animate intersection line between Objects

I am currently doing my first steps in UE4.
I would like to create a toony water where intersecting objects are surrounded by a white animated foam.

My Problem:
I would like to replace the white constant gradient with a foam that changes in thickness randomly across the intersection to make it look more natural.

Quick draw what i want to achieve:

The intersection is calculated by a Lerp between White and Blue whereas the Alpha comes from depthFade:

I tried to dynamically change the FadeDistance here by multiplying it with WorldPos / UVLayoutToWorldPos but that did not work well :confused:

Maybe someone could give me a hint / link / idea who to change the thickness?

updated initial post, changed title to clarify what iam looking for.

The easiest way to achieve that is to use a noise texture to modulate your depth. Simply add the texture to the alpha and play with the intensity of both to achieve the look you want.