How about this doctrine: ...
It would certainly work, since the MIRVed warheads will be almost impossible to intercept at that speed... unless the enemy can spot the size-20 drones in time to knock them out before they seperate.
It's a pity that you can't pack a bigger punch into your warheads, though... strength-3 only penetrates one layer of armor.
I've been having some success with size-24 planetary bombardment monitors, for knocking out enemy PDCs at very long range. I use two different types of MIRV missiles, with different speeds and travel times. Since my launchers are not heavily miniaturized, I can fire a salvo of the slower MIRVs, reload, then fire a salvo of the faster MIRVs. If my range-to-target and second-salvo firing delay are calculated properly, the faster MIRVs overtake the slower MIRVs just as they reach the proper range to deploy their warheads. This puts two full salvos of MIRVed warheads into a single time-on-target barrage, saturating the opponent's point defense and guaranteeing that plenty of warheads get through the PD screen, no matter how tight it is.