If you raise its top mounting point, you have effectively "shortened" the strut.
Actually, if you have lowered the rear of the car through shorter springs and run stock length rear struts, you can put those struts in the "correct" operating stroke position by raising the point there the top of it mounts to the car.
In the long run, you will preserve the integrity of the strut by allowing it to not travel far outside its working range.
You can also run shorter struts.
Cheers.