The fact that it's smaller changes two important factors for trigger systems - mass and geometry. Geometric differences for things like sear engagement or even travel of the striker before encountering the block can change how it functions. Mass is another critical element when it comes to dropping it and how the parts could move to release the striker, etc. These are the types of changes they tried to implement in the FCU update for the P320. The P365 is a completely different design for the FCU anyways. For all we know the fatal difference could be that the stamped housing for the P320 FCU flexes in a certain way to trigger the disconnect while the P365 is machined and doesn't flex as much or in the same way. Whether or not something like that would scale without affecting the desired weight or dimensions, I dont know. It certainly would affect price for larger stainless billet and more machining.