I believe the best thing is to begin with the 7-1/2" brace height. You can find the "sweet spot" by either twisting or untwisting the string to try various brace heights. I bet you will end up somewhere between 7-1/4" to 7-3/4".
Another thing is you may also need to experiment with moving your nocking point up and down. Start about 1/4" above the arrow rest and experiment with it from there.