Can you mount both sets of mics in the same config, one on top of the other? That way the mics on each side will have the same arrival time (phase). Comb filtering (phasing) would not be an issue when you blend from one set to the other. If you set them up with one set at 20cm and the other at 30cm, the arrival times on each side are different. Sorry if you get all this and I'm just misunderstanding your post "NOS + DIN".
-MIQ