I suspect it actually went something like this:
Jaffa curls up on the back of the sofa cos it's soft and squishy and one of his favouite places, Mosi comes over to him, a grooming/dominance lickathon follows but instead of ending in fisty cuffs it results in Mosi lying down beside Jaffa and Jaffa decidiing that's ok as long as he doesn't get too annoying. As they sleep and sprawl out, they get closer and closer to each other and sort of melt into each other with neither feeling inclined to make an issue of it, esp if there's no heating on and it's beneficial to cuddle up
I remember when they went to the cattery together a few years ago - I had said I was unsure how they'd be together in a confined space. I returned to be told they had not only been fine, but had cuddle up together a lot of the time.