Quote - You want some kind of map to give you a gradual falloff at the border of the lip, otherwise it will be razor-sharp and terribly obtrusive.  Here's the map that I use:

http://sites.google.com/site/fleshforge/Home/free-stuff-1/v4-lip-mask-bitmap

Making bump fall off that way is something that never occurred to me but is a great idea, I'm gonna do that.

Just to enlarge on Paul's thought, the mask needs to all be within the perimeter of the lip material zone. And then, if you use a shader, it needs to be for the 1_Lip and 1_SkinFace zones.

Monterey/Mint21.x/Win10 - Blender3.x - PP11.3(cm) - Musescore3.6.2

Wir sind gewohnt, daß die Menschen verhöhnen was sie nicht verstehen
[it is clear that humans have contempt for that which they do not understand] 

Metaphor of Chooks