try hanging a bugger below the popper.I've caught plenty of spawning carp using this method.I think the males get aggressive coz they normally hit the point fly(I use dragon fly patterns)hard!Cast your rig out amongst the fish and wait till a pair swimm by then retrieve your rig in short strips to get the popper working,I think theyre attracted to the commotion and grab the point fly to remove the threat in the same way as a bass will remove a lure from its nest,only with a bit more aggression(more of a killing blow than a gentle pick up and remove movement)
Hope this makes sense!
Tight lines!
Adam