I asked a state trooper about this and actually photocopied the law from the handbooks they carry around in their cruisers. According to Mass law, 4x4 vehicles are allowed 1-2" of tire hang beyond the flares. That being said, it is up to the inspector as to whether or not he will pass you. Even with the paper in hand, I had a guy refuse to inspect my vehicle because he said he'd have to fail me (this was the same guy who passed my rig 12 months prior no questions asked). I went to another place and they passed me no questions asked. I didn't even have my doors on and he said "you wear your seatbelt, correct?" Allegedly, the state is cracking down on inspectors and a pass grade to a vehicle the state deems unworthy is a $10,000 fine.
All depends on where you go. The laws in this state are so unclear when it comes to this stuff, some people will say you need 100% coverage, some people will say you don't. My recommendation? Pick up a set of old Rubicon flares on CL and throw those on. They'll give you an extra 1" of clearance.