Bantam door sizes

[kitchicken]

I have 2 size chickens, layers (isa browns aka sex sal link) and mixed bantams, they both free range on the same property. Although they share the same coop they are separated in the coop and have different doors. My problem is I can't keep my layers out of the bantam area, they take over their coop, eat their food and are a general nuisance! I have tried putting a board up in the middle of the door to keep the layers from squeezing in but after a few tries they manage to squeeze in! Any suggestions?

 

[TTracy]

Is there a reason why you are keeping them separated?