The yin & yan meeting is within. Only for physical procreation it is external.
Once when that is achieved one has to revert. While at external level our efforts should be to go internal through the gates of love & joy. The product of internal procreation is nectar of bliss & oneness.
The internal meeting is more significant. Being easer to comprehend, the external is only the basic necessity and preparatory ground for the real path which is internal procreation of oneness.