I'd think running them as 1-1-2 would be best in
CAD, or 1-1-1
CAD with 1 Allied. While the added
BS from a single battery of 3 is nice, an
MSU list will be able to force you into overkill. Better to have them in separate units so you can move fire to Target B when Target A is eliminated by the first
TFC.
Course, if I had 3 more
TFCs, I'd run them 2-2, with the 3rd Heavy slot filled with a battery of 3 Rapier Mortars, but that's just me