Mark I believe the step you are talking about is the bolt seat. I would not grind on this or your bolt will not seat correctly. As a matter of fact when you change out a barrel, a gun smith has to face the bolt to match the chamber.
However you brought up an interesting point. What ramps the bullet on the Mini? The magazine ramps the bullet into the chamber by a pinching action at the last 1/8" of the feed lips. If you load a couple of rds in a mag. using your thumb to simulate a bolt, applying pressure to the case head, and observe the case "shoulder", it makes contact with the fwd edge of the magazine and kicks up slightly untill it reaches the case "body", where it remains on this plane, untill case head reaches the last 1/8" or so, then as you continue to apply presure to the round it will jump up at you (ramping). This last second ramping is caused by: (1) proper follower pressure on case (proper spring tension, and "free" movement of the follower) (2) Shape of the mags feed lips esp the last 1/8" (3) proper angle of mag to bore pitch i.e. mag latch length to align center axis of round to chamber axis.
So that is why the mag lips shape, freedom of the follower movement, and mag latch length is so important, and why mass quanity produced aftermarket mags need some tweeking here & there. Hope this helps some.