Several questions and a tag...
Tru-glo lists, or at one time listed a set of #8r/#6f for a Sig220, I see you only have the 8/8. Can you get the 8/6?
Also Im curious as to the issue with useing a TFO front, a #6 sig in my case and a fixed plain rear? say a Warren carry cut rear.
My sig currently has a 14yr old set of factory Trig's 8/6's...............Udog
ETA:FWIW the new 226 equinox(sp?) comes factory with a TFO front and Siglite(Trigcon) rear, Im guessing that sig has no issues zeroing the equinox.