It was an adjustment in that it was promised in every coaches contract at a certain date. Maybe not a COL adjustment, but a standard adjustment for many coaching staffs.
"Should Iowa win seven games, participate in a bowl and finish with a graduation success rate above 67.5 percent, the assistants will enjoy an 8 percent pay increase next season. If Iowa finishes in the top 25, it grows to 10 percent and raises incrementally to 20 percent should the Hawkeyes win the national title."
It's no coincidence that Brian's was the smallest by a substantial amount, both in terms of pure numbers and percentage-wise.
Continue to be upset about it if you want, but you asked for evidence and I provided it. He was certainly not given a raise for his performance like you insinuated.