The sizes I indicate are just guidelines for general fitting, the jerseys go up equally in increments, however I have a 40" chest and the long zip jerseys are a body fit in Small, a race fit in Medium and a relaxed fit in Large. Its difficult to represent the broadness of fit in a small set of numbers.
I did increase the sleeve length on the long sleeve jerseys a while back as a result of feedback but the jersey sizing remained the same.
What's the arm pit to arm measurement of your original jersey ?
Just measured it, 20" from pit to pit.