I doubt it. I've never taken apart a GM MAP, but there's no rule that says atmospheric has to be in the middle of the range. Then again 99% of GM cars that use a MAP sensor never see boost, so the highest they can read is just shy of atmospheric.
1 Bar is a little over 14PSI, so 3bars is 43.5 pounds of boost.
An inch is right at 1/2 a pound (that's why the FP only drops a few pounds when you reconnect the vac line at idle)