The issue with FITs payments and TIC/DNC are discussed elsewhere and I'm coming around to the idea that the maximum output of your system is what is important and not the total installed panel output of the system.
The recent written statement from DECC "clarifying" the FIT situation (or rather describing a backup plan to introduce the 21p rate on the 3/3 if they lose the court case), did initially list the bands as being based on DNC, but this was quickly corrected to list the bands as being based on total installed capacity.