It's good to see so many bike on bike setups
I've made bicycle racks for three of my motorcycles, and all have used different setups depending on the bike.
Triumph Sprint bike rack attaches to the OEM pannier racks, homebuilt (for Givi) adapter plates, and SW-Motech top rack.
FJR 1300 bike rack attaches directly to a Givi top rack
The Aprilia Falco rack is a bit more complex than the other two and attaches to homebuilt pannier racks and rests atop the pillion.