Yeah, pretty useless at that height even allowing for zoom issues. Might work with more zoom for licence plates but for persons, all you're going to get is a view of the the top of their head or a hat. Needs to be much lower down just above head height. If you're camera coverage is correct you needn't worry about them attacking the camera, because they'll have been caught on video long before they get close enough to cause damage.
Personally, although my experience of CCTV is limited, I'd have said this might be a job for a PTZ Turret and Trip zones, because then you can have the wide view but get the camera to zoom in on the car and track it as it approaches thereby increasing the pixel density and giving you the best of both worlds. ie the wide shot when no targets are in view and the close in highly identifiable view, when tracking a target. To that end you could even leave the camera high provided you have a lower down camera to catch anyone approach the property close in.
