This is why I utterly loathe maps that have a heavily armored enemy commander. Sending out units to reinforce past a certain point just strings your forces out into a helpless mess. It's a big 'ol "Fuck you, eat the repair costs" for your front line tanks, and kinda a dick-ass thing to add into a difficulty-ladder based event with repair costs enabled. All you can do is let your front get wiped out and hope you have a good enough reserve to defeat the resulting enemy death ball.