Thats weird about the spacers.
My group buy subframes came only with rear spacers, to be fitted between the frame and the floor, to accommodate the longer bolts.
I fitted the frame straight to the floor, with the spacer above so the bolt still fits. After 400 miles sitting on the seat it is now *almost* as the standard seat.
Graham perhaps if its still too high for you after a thousand miles, you could get a trimmer to remove some of the foam from the seat base? shouldn't cost too much I reckon.