UE 5.1 Path-Traced FX issue : Heat Haze

I’m trying to create a heat haze effect with the path tracer, however I’m running into an issue with the refraction, I don’t seem to be able to smoothly blend the value of refraction and end up with a very noticeable edge around the effect

If anyone knows a fix for this, or another way I can create a heat haze effect that would be greatly appreciated