I have rewritten that post to address your questions. Especially see #6 and the links there.
– A key point is that cuti-patisandhi takes place in a citta vithi that starts with an arammana coming to mind. Thus the starting point in PS is “vedana paccaya tanha.” As we have discussed, that is “samphassa-ja-vedana paccaya tanha” in the niddesa version of PS.
– A patisandhi is grasped only if one generates “samphassa-ja-vedana.”
Please feel free to ask more questions. This is a bit complex subject.