Modifier 22 reimbursement

My physician had billed a 35556 (femoral popliteal bypass) with a modifier 22 attached. He is requesting to be reimbursed more because of the patients morbid obesity, the operating time was increased 60 minutes more because he had a hard time exposing the patients saphenous vein and arteries for the bypass he performed. How do you determine how much more of a reimbursement to ask for from the insurance companies or do I go directly to the physician and ask him? Any input on this would be greatly appreciated!