Hmmm.. I'm not sure about this c/c required thing.
When I went on MYT Lite from BHX to BVA the aircraft had just arrived on stand from ALC (packed full) and then proceeded to do our flight with the same crew, with about 50-60% load.
One cabin crew member, however, got off and went home. I can't remember whether that left us with three or four though, four I think.
I doubt MYT would fly an aircraft with more than legal minimum cabin crew on any sector, so why was the extra crew member needed for the previous (fuller) flight if the regs are only about number of seats?