While I agree the hook size is too large, do you use barbed or barbless? Personally I think barbless do more damage, especially to smaller stamp of carp. I made this observation on another thread.......but got ignored!
I reckon it also has something to do with the age / maturity of the fish. In my limited experience the smaller carp (say 4lb - 10lb range) tend to go off like an unguided exocet missle, all over the place with lots of head shaking. Although my "bigger" carp are in the 15lb - 20lb range, they tend to fight very differently, using their bulk and power in longer surging runs.
Two weekends ago I had a couple of 15lb fish plus some other smaller ones. There was more damage to the barbless caught fish of the two 15's (one of each), however all the smaller fish had a fare bit of bleeding irrespective of whether it was barbless or not (size 8 ESP raptors).
Also, I just think the larger fish have tougher mouths........bit like older slappers really!!