i have build a lot of COOP mission (sure , no MDS...)for the VOW in the past.
missiongoals very often not easy, indeed.
we worked the following:
the game count at missionstart the objects that are IN the circle.
so we used submerged submarines
at the barrier of the circle.
so, if there were 12 tanks (3 troops) and the goal was to kill 6 of them than we used 6 submarines and set 100% or 12 Subs and 50%
other way was "destroy" 50% of each troop = 3x2 tanks.......
the game has its limitations in its winconditions....... anyway, to make the circle bigger of the "destroy ground" would be a good idea !