Chicken from different runs free ranging?

How do chickens who live in different runs get together when free ranging?
I have a happy little flock who live in a cube, but that itch for more hens has been surfacing and I am debating getting a eglu for a couple more. If I housed these separately would they fight if they were free ranging with the others, my feeling is yes, but I have never kept my flocks separately.
My main joy of hens is watching them rampage my garden digging up the borders and dust bathing in my pots! I don't think I would want more if it meant that they couldn't do this. Any advice welcome from equally chicken mad folk!  

hi chuckmum! i started with a coop and run and have 5 girls in it. i added another coop and run for 3 more girls. both coops and runs are close enough for all hens to see each other and comunicate.  they remained like that for a couple of months and then i let them roam around the garden together and as treacleminer says - they initially stayed in their own gangs but then started blending together and returnmed to their own coops at night! we now have a very large enclosure that both coops and runs are inside. the girls are out together every day and behave as one flock..but funnily enough return to their own houses at night! - they dont care which nest boxes they use for their egg laying though! 

The breeder I bought my girls from has 5 coops and they all freerange together but return to their own coops at night.