Also, for an exercise that will expand the scope: hold out your jab like a feeler and see if you can throw your rear properly while someone steers your lead arm towards the rear one. You'll find even moving it a couple of inches will stop the rear shots power and make you react differently.
Thats monitoring the rear arm and with practice you could do it blindfolded no exaggeration. Everything he tries to do with one arm you can feel the intent and slow it through the other one. Best way to disrupt someones balance is to move one of their legs or shift one of their elbows, it also ruins good punching technique. Its not the be all and end all, the situation may not even arise in some fights, its just something to explore and keep in the bank for the right time.