We have 4 hyline chickens and 1 rescue orpington (I think, not 100% sure), and another big-ish brown hen. Earlier in the year we had two silkies but one was a roo so we couldn't keep him, so then we just had the one girl. When we had our roo, he kept the other girls in line so she was ok and ever since she started laying eggs she actually became really tough and really hold her own. So I don't know if its our flock composition or what but she was totally okay by herself.
Then I got my 3 new silkies (the ones who laid the eggs today!!) and I always kept them separated when feeding etc but lately they've all been co-existing quite nicely. They have their own coop in the shared run area but at night if I let them decide where to sleep they will go with the other girls!! Before this happened they were too scared to eat together with the other hens but now they don't really get bullied at all (except by the orpington who is a bit mean, but she won't peck them seriously its only a warning kind of peck).
So yeah, I don't know if my other girls are "large fowl" but Ive never had a problem personally with mixing them!