imap and opacity mapping.. help?

[super gnu]

ive added a plane with a fine frit pattern to my windows.. different dot densities in different bands. rendering now gives me a very blotchy imap. this i can kinda understand because the light is coming in through a mesh of 1mm dots.

however i decided to be clever and replace the dots in the opacity slot with a flat vray colour in the correct grey level, for the gi calc and main render (dots rendered separately) , so the same overall amount of light comes in, shadows look ok, but its not dealing with superfine dots.


imap is, if anything even more blotchy. any suggestions? do imap and opacity not play well together? does stochastic opacity sampling cause issues? should i use a map in the refraction slot or something instead? ive got almost no time to resolve this so any help appreciated.

[svetlozar.draganov]

Would it be possible to attach a stripped down version of that scene along output image(sequence) of the result you've got so far for investigation?