Welcome! I'm new here too. My experience is,my bantam rooster is also smaller than all of my hens except one. The bantam hen. At first,she was the only one he could mate. Because the other girls were not only too big,but wouldn't allow him. I think he felt inferior to them and maybe even afraid. They're mean!! My hens were setting on clutches but no fertile eggs. That's frustrating,I know. Until just recently,I had my first hatchlings! And now have 2 more brooders. Be patient. He is trying! If you put a hen and him in a pen where she can't escape him,might have better luck. I guarantee you he is trying. You will have success soon. I'll pray it's not too long. As the experience with chicks is most heavenly! God Bless!