Sigh. I think Insane Beard has muddied the waters here.

Stigweard suggested that "Perhaps that is why we struggle to see the truth of Green Men and foliate heads; we need to be looking back at a our old folklore to gain insight into these intriguing figures." He was clearly treating "Green Men" and "foliate heads" as separate entities, and suggesting that both of them could be understood with reference to folklore.

Then Insane Beard leaps to the rescue, once again asserting the folklore has nothing to do with it: "The folkloric context for the Green Man is a bit of a red herring as what we are dealing with here is a didactic icon integral to the architecture and theology of pre-Reformation Roman Catholicism."

Insane Beard has it kind of backwards, though. What he meant to say, I think, is that applying the folkloric context to the FOLIATE HEAD is a bit of a red herring. The GREEN MAN proper is not any kind of didactic icon of church architecture, but a folkloric character, specifically one from ritual drama and pageant, as I've pointed out above. The character is a very, very old feature of folklore and literature, and the name "Green man" was common for the character in English by 1578.

Insane Beard does not think there are shared meanings between the Foliate Head and the Green Man proper. Thus, he thinks the folkloric context (which includes the Green Man) is inapplicable to the Foliate Head.   

IB also discounts as wishful thinking the idea of Lady Raglan, that the foliate head is in fact a manifestation of the same character as the "green man." However, current scholarship suggests that Lady Raglan was at least partly right. In several artworks created between the 1300s and the 1600s, such a connection is implied (it's all detailed in the thread above).

My own position: while the jury is out on the strength of the connection, there is indeed a connection between the Foliate Head and the Green Man.

Thus, I think the jury is out as to whether looking to folklore can shed light on the Foliate Head. But looking to folklore can surely shed light on the Green Man proper, as Stigweard suggests. There's no need to leap on his comment and discount it immediately, as IB seems eager to do.