Even taking it in another turn and notching the bottom to clear the buffer retainer pin isn't gonna give you 1/4"that you need, or even the 1/8" to prevent contact.
Smart pic, on the bottom-good thought process. You can see that the BCG body steps up in size at 7 1/8" from the end of the buffer bumper - which will compress, slightly. They don't move much, but they move a little bit. That just tears up lower receivers...
Quarters are 0.069" thick, and one inch in diameter. They fit perfect inside the receiver extension. You'd need a minimum of 3, probably 4, inside that receiver extension to get it closer to a 7.000"internal that it should be at. 3 slightly under, 4 slightly over, that 1/4" that you need to take away in BCG travel.
I've seen 7 1/4" extensions from them before, as well as 8.000"internal, 7 5/8" internal, and 7.000" internal. I've seen some 7.100" internal on the Aero Precision M5 carbine recoil kits, and that even causes weird function issues.