Intake Backfires

So im having a debate with a local friend about nitrous oxide and he is trying to tell me that with too much spark advance (even on a stock LT1), the charge can detonate and cause the flame to travel BACK up the intake as an intake backfire.

I really dont wanna say he is wrong, because I have ALOT of respect for the guy and hell... he has a nitrous fed 396 LT1 running in the 9's, so I would assume he knows a thing or 2 about nitrous.

I just dont understand how a motor can backfire up the intake valve once it is already closed. On a stock cam, the intake closes at ~30* past BDC and the spark is advanced roughly 30-40* before TDC, which gives the crank NO LESS than 110* between the time the intake closes and the spark comes. Even if the intake does bounce, it doesnt bounce for 110* of crank rotation.

How could that be possible? Am I missing something?

So I think I have it figured out.

Intake backfires happen because of the too low RPM and pressure changes in the manifold due to VERY cold nitrous. When the nitrous is injected, the pressure drops with the temp in the plenum. At low RPM the air is moving too slow, when overlap happens, reversion happens and exhaust gasses trace up the intake into the plenum where they ignite fuel and air causing intake backfires.

Any ideas?