Seabass,
I had this VERY thing happen during my divorce in Florida. I was in the military at the time, and per diem was not a constant source of income and did not show up on my pay statement, so it was never an issue.
Fast forward to a later recalc of child support. I'm now a commercial pilot, and per diem is paid for every day of every trip, and it shows up on my pay stub.
Same lawyer, same state, and she was trying to tell me that per diem had to be included. I knew it didn't, but she wasn't taking that for an answer.
USMCFLYER, the lawyer isn't always right. They're just as lazy as anyone else. Follwing my "I can't be the first person this has happened to..." mantra, I researched the issue online and found multiple Florida caselaw citations in Findlaw supporting my position. Showed her all that material and she came around. She should have been paying ME. And I wonder how many other guys she helped pay more child support than necessary...
So, Google is your friend. Your state may require it to be counted, but then again, they may not.
Assuming your divorce lawyer knows everything there is to know about divorce law in your state is one of the biggest mistakes you can make in the process... Add potentially very costly. Do your own homework and stay on top of them.