My sound boards vary slightly from front to back. I tend to round them toward the front of the call (seems to help with the kee-kee due to the angle that the paddle is hitting the sound board), and leave them a little flatter toward the back of the call. That is not always the case, but I can usually get a wider range of tone by doing so. Just don't round them so much that it becomes a sharp point. It will turn a yelp into a dry heave.
Todd