power = the attack nano that lands. But it decreases by 1 for each turn of flight.
mass = the number of warheads. This is the number of individual hits when the drone hits.
So a power 6 attack drone, with mass 3 will score 3 hits of power 2 each. So, the first turn it hits, the next turn it destroys 3 systems, and the turn after it destroys another 3 system (unless antibodies are deployed).
If, however, you used a 1 mass power 6 drone which hit, then it would hit on the first turn, and then destroy a single system per turn for the next 6 turns.
Adding warheads means you kill the target quicker.
Obviously having more warheads than power is silly, as some of them would do 0 damage.
Mines work the same way - you add power, and you add mass for warheads.
