I think it was probably so they could use the same pressings for both as they transitioned from the SPFC to the Powertorque. I can imagine all they had to do to fit the PT to the same stamped out base was to cut out the larger circle, effectively removing the smaller mounting pattern for the FC and then drill as required for the larger PT bolt pattern around this enlarged hole.

Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!