Hi Woody,
with the air intake I go with you – if you have less then atmospheric pressure infront of the sc, you lose air mass flow in this percentage.
Behind the sc the things are not so easy. You should lose far less with a restriction. One sc rev is a nearly constant amount of air. The rev ratio sc vs. crankshaft is constant. You lose pressure if you eliminate the restriction but shouldn’t gain much air mass flow. If you had a turbo the things were different – the turbo revs just faster, you would gain much air mass. The gain on the low end must be something else.
According AFR – I think this should not be an issue with stock tune if the car is unpullied.