This is really NOT the case according to my experience.Yeah definetly will,i heard some folks say they are less agressive with a duo,so i got curious and made a thread.
I gave a friend a pair of Lavender Silkies. That pair sticks together among her large mixed flock. The cock avoids her other roosters. But he attack my friend every time he gets the chance. My son who works for them also get attacked every time his back is turned and has taken to punting him like a soccer ball into the fence. I am completely appalled not only by the behavior but also by the fact that her husband will not allow this idiot of a rooster to be dispatched. It is NOT cute for little critters to attack people. I now regret giving those hatchery chicks to my friend! Maybe if you get one from somewhere that selects for demeanor in their parent stock is a good idea. Yes, I repeat... Silkie, the claimed most docile breed!
But I would not personally get a bantam boy to "roam 15 acres', as I may never see him or know if he survived. If I was going to get a duo... I'd make it a trio and give them their own little set up where I KNEW I could interact with them on a regular basis.
I've raised a couple hundred cockerels with a large portion being bantam... The bantam boys are every bit as hormonal and stupid, if not a tad more stupid than large fowl boys. But again, each is an individual and ya just never know.
They recently offered me hatching eggs from that duo, even to sell... I said NO thanks... attitude breeds forward!
I keep bantam and large fowl roosters together all the time on less than an acre, regardless of breed. Individual attitude effects flock wide dynamics.