The big difference is the political availability of extra forces to the Tevs. A new Deimos or three can be sortied through the gate with little fuss, it seems. Sending a FrigRon from 1st Fleet to support 3rd Fleet and militia elements is both much less likely to happen, and decidedly more of a political move, with all the disadvantages (and, granted, sometimes advantages) that entails.
And it's more of a case of the UEF not knowing exactly if such Deimos, hell even more Hecates or Raynors, are en route or not, and they have to calculate their tactical risks with this big unknown variable lurking in the dark.
In such a scenario, it is much more intelligent to play the kind of "hedgehog tactic" that, for instance, Kasparov used in his first game against Deep Blue (where he actually raped the computer to smithereens). That is, keep astonishing "low ball", concentrate your resources and keep movement to the minimum possible way, deep back at the defense. Only when you see a deep clearance far ahead in the moves, you go for the kill.
Curious. As I think of it a little better, this WiH war is very analogous to
blind chess, with one side having less pieces sure.