When the Independent Group chose to assemble for battle, the Empire, having failed to eradicate them, continued using the previous tactics.
Simply put, it somewhat resembled the Change Home Tactics.
Allow the Independent Group to attack the Empire's frontline positions, sacrificing inferior troops to intercept, while concentrating superior forces at other frontline positions to launch assaults on the Federation's positions.
In the entire western war zone, apart from the Independent Group, there simply were no forces capable of blocking the Empire's superior troops.
At that time, the battle zone was very close to the Empire's Transition Base. The Empire's support and logistics supplies, as well as the arrangement of various reconnaissance facilities, were all more complete than those of the Federation.