It really depends on their forage. Out here on my home waters, if i put the fly 4 feet away from the fish I would never catch a carp. Their primary forage is freshwater clams, so they do not have to chase or pursue any prey. I have to get the fly within about 8 inches and then for the most part I just leave it there until they find it, and suck it up. They will only hold onto the fly for a split second because carp have a HIGHLY developed sense of taste. you have to keep in mind that they eat mostly by "tasting" a batch of sediment for food. They actually have a tongue inside their mouth (it can't extend) that they use to trap real food inside, and then they blow or eject the debris either out their mouth, or out their gills. this whole tasting process lasts less than a second.
So the real trick is to present a fly that will visually stimulate the fish into ingesting the fly (not easy, as they primarily graze along and simply trap food and eject debris) and then seeing the moment they take the fly and setting the hook at that exact moment.
Blind casting can be effective (not on my waters...) depending on their forage. if they are used to pursuing food and visual hunters, you can likely feel a take that way. if they are grazers, you will need to present the fly much closer to the fish and find some visual cue to detect the moment they ingest the fly. i know some guys that use strike indicators to help with this in murky water, but I have the bets luck by only casting to fish i can see (even if i can't see them clearly) and then watching for changes in body posture etc. and using those changes as the cue to set the hook.
especially in cold water, they are less likely to pursue food. It really comes down to knowing your forage. In my situation, i can count the number of takes i've "felt" on one hand...and that is in about 8-9 years of hardcore carp on the fly pursuit. i catch a couple of hundred carp a year, but the forage in my main water dictates that i simply don't get aggressive fish who will charge a fly. when i travel to lake MI, where the primary forage seems to be gobies, it is a totally different situation. we do catch them blind out there.
good luck man! I hope this helps!