These are the ways that I prefer to categorize wens (just my own preference):
Cap - only on the top of the head, and when mature looks a bit like a poofy, rounded hat sitting on top, almost as if it's separate from the fish's head
Lionhead/full-face - extends from the top/back of the head to the mouth and over the gills/cheeks, giving a chubby appearance
Tigerhead (term from a Chinese site) - extends from the top/back of the head to the mouth, but does
not cover the gills/cheeks
Crown - one or more distinct bubble-like growths on the top of the head, such as seen on the
Crown PearlscaleHere's an odd question: would the lower bubbles on a
Double-Bubble be considered a wen element?
My oranda would be an example of a lionhead/full-face type, although when he was younger he had a tigerhead type.

A bit hard here to see how it covers his gills, but you can see how poofy his cheeks are.

Apologies for the blurriness of the one on the left.