Not going to happen. Might I suggest reading up on chciken reproductive systems?
Start here.
If you want pure bred birds, you will have to keep the flocks separated at all times.
and the 1/10 ratio is a thumb rule for fertility - how many hens, on average, can a healthy mature rooster of typical breed "cover" with near 100% fertility. (Eggs may still fail to develop, of course - but they at least had a chance). If you are willing to tolerate lower fertility rates, and have a young rooster, they can likely cover more. What ratio is "too few" and results in overmating? Highly rooster dependent, and age disparities may play a factror too - older hens **seem** to put up with less behaviors from young roos than younger hens do, and can often convince the young boy to be more well mannered.