"I'll stay in the lead, so anything coming for me will come from the font. I'd suggest we keep Romana, the Master, and the .... Doctor who's not shagging the Master in the middle. The Doctor who's wearing my teeth marks can bring up the rear."
He had reasons for that, but wasn't going to take the time to explain them all. Mostly it was down to 2 people they needed, and one they needed to protect. The one they needed to protect, most likely, was not the woman. It was the younger seeming Doctor. The Master and Romana would be good for tactics, and the Doctor in the rear-- could fight.
That said, he took off walking again, up the first set of stairs.