Why not mount the cams at 20ft?
Pick cams with a narrower FOV, ie: maybe a 12mm lens.
Play around with the "
Camera Calculator"
It will show image clarity at 20ft, using different lens sizes and the FOV.
I assume you don't already have the cameras....
If you have the cams, then consider a lens change. I changed a lens, it's not too hard...
Fastb