I have been fishing a generic green soft hackle for years...it just looks buggy. Added the tail on the suggestion of a buddy and it has worked great. The thing to keep in mind is that carp really don't use vision as their primary sense for feeding. They do at times, and there are tons of examples, but as a general rule they "graze" and use their sense of taste to sort through food. I think a general pattern with multiple visual cues is likely to be effective. In the case of the hybrid, the fish can see an aquatic worm, a clam foot extended, a general nymph pattern...or specific nymphs like damselflies etc. not to belabor the point, but the forage matters. If you learn the primary forage it is way easier to come up with some effective visual cues.
My favorite fly might be totally useless where you fish...I know when I go to lake MI I don't fish soft hackles. I have caught carp in lake MI on soft hackles, but usually get a much better reaction from something that resembles their primary forage (gobies or crayfish).
The fun part is figuring this out n your water...