David I am a believer in free mating especially the racers, but letting them all in together does cause kaos....and sometimes you always find some hens get fed up and a few are without mates, what I do then is close a birds box up so nothing eles goes in it, put him in a section on his own if you have one otherwise a basket will do. Put a fresh hen in with him in the section and leave them for 1 full day and half the next day and they will have paired, then put the hen in one side of his box and let him back in the section he was in, then do the same with the next cock always works for me.
Stock birds are always different I always put a hen in one side of the box to pair when they are showing to one another after the first day I let them all out for food and a drink, sometimes out of 12 boxes 2 or 3 will click after 1 day, sometimes none at all.
If after food and water they are all over the place I put them back in the boxes and they stay there another day, I repeat this for 2/3 days, then reverse it and lock the cocks in the boxes one side and leave the hens loose. Then you will see some hens going back to the boxes they were in and the cock will be calling. then 1 at a time a cock that the hen is coming to will be let out once she finds the box and they seem happy they stay out, eventually they will all be sorted mine all paired this way this year within 4 days.