>>Basically the spent brass is ejected forward on a chute.<<
Would it function properly if you were shooting at someone who was above you?
Absolutely. The force to strip and load a new round, and lock the bolt, is much greater than the force needed to shove an empty brass case against a stack of empty cases.
And as I said, there is a flap that the empty brass passes through to prevent the brass from sliding back and jamming the bolt mechanism.