The droids reach full calibration in fewer stacks then on 8man because of more availible interupts. They might have reduced the stacks to bring it in line with 16 since most classes have an interupt now.
By the time the other 2 droids are down, your other tank should have had enough interupts to keep it below 6 stacks by himself. This allows for the rest of the raid to catch the last droid before full calibration and keep it that way with all the interupts in the raid on the same droid.
This change makes all phases of the fight "dangerous" instead of fodder for fight progression.
I'm lovin it.