Thanks again for your reply.
I read that paper, may be should read it more carefully. As I remmember they used unsynced BN and minibatch per GPU was always 32 through all their test.
So They didn’t exercises possible effects of different minibatch per BN.
Unfortunately I have  to use minibatach of 16 per GPU.
Is this minibatch big enough?
According to paper unsynced minibatch increasing makes no sense, but what about synced one?