I think I see what your saying. The lower spring perch can't be adjustable? (Cause my stock spring mounts to the lower perch of my stock strut.)
Or that any piece that adjusts the spring such as a spacer must not be part of the strut.

Yes, that must be it. I have re-read 5.b.3 "Spacers, including threaded units with adjustable spring seats, may be used with coil springs, provided the spacers are not permanently attached to the shock/strut housing.