I agree with my friend Bob.
If I were to rig my boat today, the spin sheet rear block would be about 18" to 24" forward of the transom. That will still give a very good angle for close reaching, but will keep the sheet from sometimes flipping up and hooking on top of the end of the boom. Kind of inconvient ( and slow ) to repair this when it happens
I once had a boat in another class with the turning blocks mid ship. It was an OK set up except for when beam reaching with the kite. Then the angle caused too much hook in the spinaker leach. Slow.
phill