I fish for surface carp using the three conventional methods...
Floating crust (and this for any carp over 6/8lbs) cut in 50mm (2") squares by at least 10/15mm thiick. Using a No 6 or even a 4 hook I push the hook through one edge, bring the hook under the crust and hook in into the opposite edge. In open swims I use 6lb line treated with Mucilin floatant . The important thing is you either have to cast to fish you can see OR use something that will bring them to the surface. In my case I use Pedigree Chum Mixer softened in a little water over night.
Personally, I try to get some height above the water and look for cruising fish before catapulting out a few mixers over them. Once I see interest I underarm swing the crust out as gently as possible and send out a few more mixers.
What I don't do is just cast lumps of crust out hoping for the best, particularly if the water has lots of small piranha type fish that mess with the crust.. In cases where small fish exist I have noticed on many occasions that once a carp approaches the crust the small fish scarper!! Small fish would not stop me using crust and if you only cast it out when it is LIKELY to be taken by carp I suggest it will catch you fish!! (imho!!)
The other non (crust) method I use (nothing new about it!) is a suitable controller float that will get your bait where you want in without anything more than an underarm cast. Again, I use a 10 hook for one Chum Mixer and an 8 for two Chum Mixers with no more than 3' between hook and controller. The 6lb line is ALWAYS treated with a floatant particularly next to the bait!!
I am aware this is not the case with fly fishing, but we are NOT fly fishing!!
This method works well when the bait is cast in among loose Mixers, but again I really think it is important to cast to, or fairly close to carp that you can see, on, or just below the surface.
Both methods work best when it is quiet and long casting unnecessary, with fish possibly in the margins. I have caught good carp 2' from the bank on the lumps of crust - equally I have caught 4lb fish on crust of the same size!!
Finally, I also catch good carp (same crust size) on anchored crust. I hair rig the crust, and using a 3/4oz bomb cast out close to bushes or similar. The whole lot sinks but once you release the line the crust will float to the surface and you tighten to it. Either that or wind the crust down so it is some inches BELOW the surface and just wait for the carp to find it!!
If small fish are a problem then scatter a few mixers of bits of smaller crust to occupy them.......
ALL of the above have caught fish on many different waters and none of the methods described are new in any way, shape or form, but they are proven to work with a bit of care and effort!!!
The 'secret' to my mind is finding your fish in the first place, rather than just aimlessly casting and hoping it will all work out.....................
Exciting fishing, though!
Good luck!
ps Best bread by far is a Tin Loaf from Waitrose which has good crust on all sides. Cut the crust off in 'sheets' about 15mm think and this can be then cut to suit. It also freezes well...(Asda Tin loaf is okay but crust not as 'crusty'