Good way to get IOReflecton element in one pass?

[DPS]

As per title.

So I have control over my objects in comp with multimatte elements.

So I'm looking for a method of essentially gaining a reflection filter element but one that ignores any maps that I have plugged into my reflection slot.

And of course without having to re-render elements.

I tried using a falloff map in an extratex set to fresnel and with override material disabled. That didnt work.

I thought of creating separate falloffs in extratex elements for the materials that I want control of. But the falloff fresnel appearance differs from the vray reflection filter pass. It's also a bit if overkill calculating separate fresnels for my scene multiple times.

[DPS]

Actually I think my question shod have been - how is the reflection filter pass created?

And how would I correctly adjust my reflections using an extratex element with my reflection map tree plugged in?

[DPS]

After a couple more hrs playing around I've found the solution.

Divide reflection filter by your reflection map (or the other way round) and you're left with your IOF. Wish this stuff was written down somewhere.