To start with when I got this puppy, the one behavior I wanted to start early was the sit and I wanted a very crisp sit. I started from 8 weeks old by luring. Within a couple of weeks I introduced the whistle. I then "superconditioned" the whistle sit. All this done very close. Next I started to spring the whistle on her at other distances. All this was done initially with a food reward. Once I did this, I started to mark the whistle sit and then reward with a retrieve. I just let her go. Then I did whistle sit at a bigger distance, she would turn to look at me, and I would throw to different points around her. She started to learn that by looking more directly at me she would get a better look and quicker start for the retrieve. Then I started to shape the whistle sit when I did Mini T. I would never send her for the retrieve (i.e. cast) unless she gave me a straight sit. If it was crooked, I blew the whistle for come in and then stop quickly, then wait and then send. Now for the surprise. The last couple of times that I stopped her doing T, I just looked at her and did not send her. She then adjusted herself to a straight sit, I marked it and sent her.
The operant dog will try different behaviors to earn a reward. My dog was operant just by the fact that she tried a different sit position to get the retrieve. BTW, it is difficult to extremely difficult to do with a dog that has not had any training this way. I see it in my obedience class.
Superconditioning means that the response was made automatic.
What I think is also important is that every time I use the whistle, it is followed by a retrieve at some point, even at the line.