okay it's like this kundalini seats itself in the perineum inwards in the perineal sac , here it makes a "kunda" (sanskrit for a large coil) , once awakened or activated the path to shushumana (the central canal in which the kundalini ascends upward) is guarded by the coccygeal plexus and the coccygeal muscles in your tail-bone.

{the classic pathway is this -->Dormant Kundalini --->Activation-->Perineal arousal--Coccyx gateway transmission--->shushumana--->shasrara.}

This is the very classic desired pathway for those undertaking Kriya Yoga (the yoga of energetics) , Kundalini Yoga (the yoga of kundalini arousal) differs from the former in terms that one undertakes kriya yoga first to make sure the pathways are open , otherwise it's like over surging a circuit.

This scheme of kundalini dynamics occurs very selectively .

Kundalini can even start within a knee , a broken arm , horrendous tragedy , electrocution , being struck by lightening or even by prolonged labor.

Whatever the starting point it takes , it does however desire to reach out through the highest chakra , the scalp chakra and plumes outward.Again that's the ideal aim , but it is often many many years till that happens , in the meanwhile kundalini stops here and there in your body and does what it has to complete it's agenda (which different in each case).

One of my most fondest pursuits in life is talking to people and discovering how and what was there initial trigger , the event that instigated arousal , in my 7/8 years of research into this , I got in touch with a German woman on a spiritual crisis hotline , it turns out , her trigger was a severe sun burn.

it can start from the skin say if you lay out too long sprawled on the beach , it can start from a broken bone in a car accident , it can start in the uterus when water breaks pre-term , it can start in the mind if you are given the news your entire family died in a car crash , it can start right in the spine for a construction worker drilling ground with a large bore drill.
Who's to say "my Kundalini experience is the accurate of all because it started from a particular pre-established spot , i.e perineum or the coccyx).

also that way the whole "perineum or the coccyx" question is very moot.The typical account does say people feel energetic sensation the spine , tail bone or lower genital areas but there are just many instance if not more of people feeling nothing in those parts at all and go onto have profound Kundalini experiences.
to analogize , some people feel strong vibration or buzzing before the stages preceding an OBE/AP other are just as well able to make the same separation and exit outward without any buzzing or vibration . (Your energetic construct and pathways are pretty much like your finger prints , we all have them but they are unique to us all)

good question , I enjoyed answering it.