I've observed both gaps and no gaps for different combinations of SF flashlight bodies, bezels, and drop-ins. Basically, there appears to be enough manufacturing variance that it can be hard to predict with certainty whether or not you will have a gap.
The Z32 weaponlight bezel seems to be the most accommodating, probably due to the shock cushioning. I've not had any gap for DX6090, KD2363, and OpticsHQ/TLS drop-ins mounted in old-style SF 6P, 6Z, G2, and 3P.
Second most accommodating in my limited observations is the new-style SureFire 6P bezel (the one with the anti-roll flats).
No gap for a DX6090 in a old-style 6Z (DX6090 outer spring removed). Have to unscrew the pill slightly to make electrical ground contact. Big gap with the outer spring installed.
No gap for a DX6090 in a 3P (outer spring removed). Big gap with the outer spring installed.
Slight gap for a DX6090 (outer spring removed) in an old-style 6P. No gap if I use a new-style 6P bezel.
No gap for a DX6090 (outer spring removed) in a G2. Big gap with the outer spring installed.
No bezel gap for a DX6090 in a new-style 6P bezel screwed into a TNC E2C adapter. The E2C has a small gap between it and the L4 body.
Slight gap for the OpticsHQ/TLS drop-in (outer spring installed) in an old-style 6P using the original bezel. Gap is easily accommodated if you use a SF bezel lanyard ring. No gap for the OpticsHQ/TLS drop-in in an old-style 6P using a new-style 6P bezel.