We want a clear signal for the dog to fight the helper. This would create a problem that would then need to be corrected. In every part of dog training we want to make sure that we are only training one thing at a time. So by having the helper break into an escape at the instant the dog is sent, we eliminate this potential problem. In the first steps of teaching this exercise we want the dog to realize that the instant he gets back to the handler he will be sent for a fight.
Timing is very important here.
There should not even be a second's delay when the dog returns. He must be sent instantly. Once the dog understands this concept, his recalls will be very quick. This seems like a very simple concept, but the training steps must be followed. So we need to set up the training to address these issues.