That coil is suitable for exactly what you’re using it for… an airy MTL… RDL… IMO 20W is perfect for it..
The liquid shouldn’t be making this much gunk in just 2 hours.. we’ve all encountered a “gunk factory” before, but two hours is a very short time..
I suspect the wicking and not a fault of BP mods, rather that something isn’t as it should be..
Have you been using this atomizer for a long time?
Maybe it also occurs to me that the mod is preheating the start of the puff too much.