I have 9’ ceilings is the an optimal height for MD like the PIR1 off of the floor.
Note: I have a cat as well.
I found the info.
Glad you found the necessary detail! Mounting height for each model of motion detector may vary. It is best to follow manufacturer guidelines in the product manual. The PIR1 manual can be found here.
Note that with cats, the PIR1 should not face furniture that the cat is likely to climb. Especially furniture closer to the detector.