Bait dragging the bottom Philip,there were several caught over 17lb on the float,but there are times in summer in particular when they come up to the surface and you can see them take your bait,in fact I think they use it as a ruse for not getting caught against the majority of anglers,just people like myself who have caught countless chub up in the water cotton on quickly,but the thought of guys trying to freezlining a 6mm pellet with 10-12lb line and a 1.75lb tc rod is impossible for the majority...
Let me clarify my shotting a little,I was using a 3 no.4 stick float,with a bb under the float(casting weight),a bunch of 3 no. 8 stotz,then 2 no. 8's,then two no. 10's,these two were apart for the majority of the session,these shottings were 3"-3",-3"-3" apart,from the first no 10,to the highest 3 no. 8's,im not saying its totally critical to have this shotting,but fishing a bigger bulk would cause problems,catching wise(on the river I fished on Tuesday),the float was set say 3-4ft deep,fairly quick,the barbel do come off bottom in the winter and the artist(Rob)said that the depth being fished didn't matter that much,the regular feeding of a few maggots got them cruising about looking for bait...
On the Ivel they were mainly caught on bulk shotted (3aa to 6aa,or the equivalent olivette),with two small droppers,or a small swivel.
Sorry for the waffle,geeky answer,but it is pretty important imo...