I have seen griswolds installed backwards (flow opposite the directional arrow on the valve body), even when the coil is piped correctly. This will affect the volume that goes thru the coil.
I believe that there may be markings on the cartridge that can be cross referenced by griswold.
I wonder about the original design paramaters. Design differential water temperatures are typically 20 to 30ºF not 55.2º as indicated. I would talk to the engineer about it as a first step.