Using a 12.5 aa hop with a 20 minute boil, this software shows 28.51 IBU which seems correct. When I change "boil" to "whirlpool" the utilization goes to 10% which seems ok. I then put 180 degrees for 20 minutes in and it shows the IBU to be 17.2. This seems excessive. If I change the utilization to 100% it goes to 170 IBU. Am I doing something wrong?