I prefer to look at back stance as a transitory stance, ie: I don't hang out there very long. I use it to shift backward from a more forward stance (or as a full step back), but then my retaliation is instant, whether it be keri waza or not.
I don't think the stance is the key here. I think the idea is transitioning from a defensive attitude to an offensive one, and that is what your instructor wants to pull out of you.
Calling yourself "Master" implies that you have slaves.