Caught decent bags of bream on the pellet feeder with a wafter buried in the feeder,I think you would be surprised Jim.
As for the groundbait consistency,it's about what your bait is made from too,certain mixes are far slower breaking down,also things like molasses make a stickier mix,if you are fishing for barbel feeders are difficult I believe,Jim fishes the Thames so he knows,even in summer when flows are slight,bait seems to trundle away,that's anything,even square shaped boilies,I believe regular feeding is key,smallish amounts,but regular,my most successful method for barbel on the Thames was a small feeder,like you would use for chub with liquidised bread,filled with dampened 2mms pellet and crumbled boilie,cast every 15-20 minutes,not my normal way but just kept a bit going in...another was small pva bags fished similarly.