I meant to reply mentioning the same thing in your last post where you were talking about getting the bounds of the backfacing geomtry:
https://forums.unrealengine.com/showthread.php?49169-POM-material&p=315946&viewfull=1#post315946
I am not sure why you would ever need to define the bounds using a separate pass like that. Usually you know the bounds using the bounds_0-1_UVW node like you mentioned, and you know when you’ve exited the bounds since you increment the current position by a ray size that is divided to fit your bounds. So then you just know when you are at the other side that way (the POM material is doing the same thing actually but using the camera vector math). Maybe I was not understanding the original question but I think you can get by without having it.