I don't have a lot of experience calling bears (Just called a half handful) but I hope I can help.
Bears are a temperamental animal to try to call. Some bears that hear your calls will come running, some will come at a slow trot, stopping often to chew on something before coming towards you again. And others just don't want to come eat your jackrabbit, some will run away at the sound of the screams.
I feel it's a good idea to use a larger prey distress sound to entice bears a bit more, instead of rabbit screams use fawn bawls, doe bleats or even cow elk mewls. These sounds have worked better for me when calling bears. Blow long, drawn out, hoarse screams and you stand a better chance at calling in a bear.
I really prefer to glass up a bear and then make a stalk until I am close or in his line of travel (If he had one). I will then start calling, often it is nice to be able to see him when you start calling so you can see his reaction to your calling. If I am just calling off fresh sign I will stay on the stand for up to two hours to make sure I give the bear plenty of time to get to me.
I know I've skipped over something so let me know if you have any questions.