From what I can tell, the coherency rules do not force units to form a single contiguous group. I may be mistaken, but this appears to be legal: Each model is within 1" of two other models in the unit.
"But no-one would do that! It's unit suicide!" Well, not necessarily. This setup is less fragile than it might seem. If you lose one model, the unit size drops to 5 and it is coherent if each model is with 1" of one other model. If you lose two models, take one from each group. If you lose three or more models, remove one group and the excess from the remaining group. Also, splitting up into triplet-groups can let you grab multiple objectives, and virtually risk-free in the last turn of the game.
So, is this actually legal or did I miss something?
-T10