I have found that stopping down with the Maco IR has traditionally been enough at least in the 120 size. I guess I never really looked hard at my few 4x5 shots and until I tried it in 8x10 and compared it to a Tri-X neg of the same scene (shot with a red Lee filter, I think) side by side (all shots were done with a 420 mm Repro-Claron and I developed them in Pyrocat-HD), I never really saw how 'fuzzy' (for lack of a better term) my IR negatives were.

Do you just stop down your lenses a lot or do you actually do a focus adjustment for the IR light with your LF camera? Hope that makes sense.