think if you pinned your hook length down and had a long hooklength, it would sort most of the problems out once its in there mouth, I dont think they could eject the bait even if they wanted to, likes been said every river is different and every day is different , think we all make the mistake of fishing for barbel like carp , which can make things 1,0000,0000 times more difficult , just try different hook length materials and see which one works on the day, cos no 2 days are the same
On a different note does anyone thinks it matters if your hemp splits or not ? I for one dont think it bothers the barbel as they filter feeder