wheelscrubber and ground clearance

[Reds]

I have a WW2.0 with the wheel scrubber option. The scrubber has a set of eyes mounted on the gantry to detect the front and back of each tire as it makes its first pass. I wash a lot of cars and do not have any problems with it. But this weekend I had someone go thru with a lowered car and it confused the eyes. The WW scrubbed his front wheel and then came out and scrubbed his doors, putting swirl marks in his paint. I watched it on video. The eyes are mounted 4" from slab to bottom of eye, and 5" from slab to top of eye. I am going to have signs made ASAP and need to determine a minimum ground clearance to post on the signage. Has anyone had this issue or posted minimum clearances? I was considering 6" minimum ground clearance, but am concerned that maybe I should bump it up a little. I don't want to discourage customers from selecting the wheelscrub option, I just want to convince people with lowered cars to not select the wheelscrub option. The wash with the wheelscrub is the most popular wash I have.