On lvl 6 imperium ill usually do the following meta that usually results in 1-2, sometimes 3 stars. Very versatile for a lot of base types and NO STUPID PATHING ISSUES (well, in rare occasions, the tanks are stupid...)
6 dark troopers
3 repair droids
=88 slots, have to update that last platform
Send few darks to draw focus, then deploy tanks and hero. Shields go down fast (seems that hero at-mp has some multiplyer) and turrets are attacked with good damage and range, resultkng usually in a one or two volley kill. Repeat distraction with darkies for each shield.
If the machines have to tank rocket fire, deploy repair droids, if needed use TIE to take down specific mortars or rockets.
Use the dewbacks for mobility clearing damage, walls, or to distract turrets.
Use the heavies exclusively for clearing up the safe area behind the turret squad
try to meet with machines at the hq, since somtimes machines seem to camp there, attacking the hq while taking turret fire.
One star guarantee, usually two, will be three if heavies and dewbax survive.