I see your point exactly. It almost seems that either leg is limited to 26 Amps in the 50A setup, but you can get 30 amps out of one leg only without overloading the generator.
I don't know whether if will make any difference or not, but you could try running the A/C units to give them a little prestart on the 30A plug then do a quick switch on your cable and a quick start on your A/C units and plug into the 50A setup.
You could also try shutting down the feed to everything else except your a/c's so you are not using any power for your converter, fridge (on auto) or other load grabbers and see if that makes a difference.
