I think nothing is needed besides that state of love. Two people are concentrated on personalities of each other, integrate in themselves the style of thinking, the needs and wishes of each other, study from other what to be your dual. Such you'll activate and begin study your weak funtions. It's like a student tries to imitate a teacher, but with more passion, deeper compassion, in wider degree, with some trance helping overcome protections and with much more pleasure.
But you need dual, as all other types have conflicting regions and a try of deep integration may to have side-effects. For example, such thing with semi-dual will overrise your 8th function, what may lead to compensation by 4th - probably you'll get more doubts and fears in polr.
> Maybe it's just that I didn't experience duality deep and long enough yet
The main problem is to find good dual girl and to establish relations. Then you may experiment without limitations.
For me, even having skills to find duals, this seems to be a problem. 90% I'll make a marriage with semi-dual (ESI).