Most manufacturers require at least 6 nails AND HAND SEAL of sidewall shingles (over 16-12 I believe). Why in the world would anyone not use 6 nails on any pitch? In my prime, (admittedly a long time ago) I could install just as fast using 6 nails as 4, provided I was using a nail gun. I was never a fast hand nailer and was in awe of those who were.
6 is too much imo ,5 at thick strip are sufficient.
Not on mansard. You would not be meeting specs and they would most likely slide off.
My mistake, 18-12 is the breaking point for requiring extra nails AND hand sealing.
Mansard is 6 nails , but I did 5 on 1/2 plywood and it was good ,on 7/16 prolly 6,still