best case senario i like to see, in this order:
start of breast, nipple, place where breast fades back into the rib cage. this applies to wherever you start from and whichever direction you look.
that may seem a round-a-bout way of speaking but referencing the pics above, in 1-12 the curve of the breast conceals where it meets the rib cage again. 13 and 14 do not. 15 is not breasts, but lack thereof. that is fine too.
at the end of the day, anything between 9 and 15 will get no complaints from me.