gunga64
No mine are at floor level. I hot glue an ActiveEye, EagleEye, etc. to the back of a 2-D cell battery holder and power the mounted Motion Sensorfrom the D cells. I stick some rubber feet on the bottom of the holder. The D cell MS "package" will now stand upright and it allows me move motion sensors around the house when needed. The disadvantage is, the battery holder prevents the MS package from being mounted by screws through the back of the MS.
However if you use the MS outside, I think you are correct in thinking it will work better if raised a bit.
I think you may also have some problems with small animal detection during the day in the summer months.
I use one of the described MS packages on back patio as a raccoon detector near our humming bird feeder. Apparently word around the raccoon neighborhood is we have opened a free juice bar on our patio. It works fine at night, but during the heat of the day it has trouble seeing squirrels, sometimes it triggers, most times it don't.
But good luck.