My rationale for installing 2 on each side is that it will disrupt the "flow" of the customer as he/she has to now walk from one side of the bay to the other. As all we are selling is time, it might help add up.
How long until you can retire on the extra $$ you'll make by manipulating people into walking 10'? Customers do notice little things like this and know/think that you are manipulating/tricking them into spending more money.
I built a wash in 2004 that had the wand on the opposite side of the bay from the Foam brush. The nearest competition had both the HP gun and Fb on the same wall. It wasn't more than a week before some guy was yelling at me because I "purposely put the brush on the other side so it would take him time to walk around the car while the timer was running". Fortunately, i was quick to respond something like "It is a trick but not what you think...It takes about 8-10 seconds for the foam to reach the brush head. If you grab the brush right away and start rubbing it on your car, you put 6-8 seconds of scratches on your car because you are using a dry brush". His attitude quickly changed
Don't get me started on the FB
soap named "Cling" with the description on the side of the drum that said "a difficult to rinse FB
soap so your customers have to spend additional time to rinse".
Just put the mat clamps next to the existing clamps and spend time on something else