T prove how inconsequential diaphram covers can be, on another site Altavillan shows a diaphragm cover with almost the entire center of the cover removed. He flies it that way with no problems in his Sukhoi.

The point is there isn't much of an issue, if any at all, with diaphragm ocvers and pressure 98% of the time. People seem to go out of their way to make one though.