After the collapse of the outer defensive sphere, the First Armada did not press on right away.
A lull in the fighting ensued as both sides began to recover and take stock of the situation.
The alien defenders were more than content to use the available time to reorganize their defenses, analyze their enemy's weaknesses and recover their morale.
The human attackers recovered their injured and escaped personnel while also replenishing their mechs and other combat assets.
The leaders of both sides knew that the second round would become a lot more intense.
The First Armada had undoubtedly won the first round in a crushing fashion, but it had lost the advantage of surprise.
Sure, the aliens suffered a lot of material losses, but the units stationed in the outer defensive sphere happened to be the weakest ones in the star system.
The middle and inner defensive spheres possessed a much higher priority on newly released tech!