Hello 11jono11,
Some people (or systems such as ashtnaga vinyasa yoga) refer to the perineum/perineal body as the seat of mulabandha.In males that is.In women also some might refer to it as the opening of the lower vagina(i.e below clitoris) or inner cervix/vaginal muscles just inside ,to be precise.This may be the source of some people's confusion.
The relevant lesson(Mulabandha:-
http://www.aypsite.com/plus/55.html) refers to the anal sphincter though i will say a later relevat lesson does refer to anal sphincter/perineum or both.
My comparitive assesment (of AYP system) has been that there is probably adequate stimulation affected through siddhasana and root-to-ajna spinal breathing to probably obfuscate any imagined need or necessity for physical contraction of the perineum. And i think this is a fair assesment.Yogani talked about alternate flexion of anal sphincter as ashwini mudra rather than just contraction/flexion itself.And like i say in later lesson he referred to either or perineum/anal sphincter or both.Some folk speak of pelvic floor muscles(i.e altogether collectively) and a simultaneous pulling up, just like uddiyana bandha;Always inwards & upwards.The same of mulabandha.I'd imagine one pulls like you say upwards through the space in the pelvic girdle in terms of what aactually occurs physically . Also bear in mind these actions refine so we just have to entertain the impulse and a mental contraction or psychic connection can be made.
Of course it does'nt matter what terms we hang on particular actions,be they physical contractions or mental contractions (i.e subtler still).They all are designed to contribute to the rise of energies upwards, particularly sexual,enliven the spinal nerve and of course stimulate the arousal of Kundalini,located at the base of the spine.The development of ecstatic conductivity.
When i did my spinal breathing i contracted the anal sphincter ,just like it says in the lessons.
I had this same lack of clarity and i hope i might have dispelled any confusion.
The lessons explain really well what is involved.Yogani seems to have a special knack for clear uncomplicated explanation.
Of course,If there is anything you wish to clarify again or further on this or any other topic ,just say.