If your brace height is 7" and your draw length 30" , then your power stroke is 21 1/4" .
If that brace height is decreased by 1" , your draw length remains 30" ...
It is not quite that simple to just decrease or increase the brace height and let everything remain the same. In order to change the BH on any given bow, several things have to be changed. They would include changing the limb length, changing the limb deflection (which would change a lot of other things), changing cam design, and even possibly changing the riser design. Therefore, it real isn' t that simple to make judgements until all the above design changes are considered.