I am pretty new to this breeding game myself but I left my knoblochi together for breeding. They are pretty close in size and I watched them pretty close for a while. One piece of advice I can offer you is that if you keep them together make sure you seperate them for feeding. I was feeding my female a mouse when she missed the mouse and grabbed the closest moving object instead---the male's head. She started swallowing as well. I grabbed her by the neck and she opened up and he pulled his head out of her mouth. She then found the mouse and ate it while he waited for her to finish and then bred her again.