Agree with not putting them in front or behind the SS bays. Mine are at both my washes. I don't like busy days where bays are blocked from customers using the vacs. Not their fault, just a design flaw. I don't like them behind the bays either as I feel bad as people with clean, dry vehicles are vacuuming and someone in the bay is washing and the wind whips through spraying the other customer's clean vehicle. In my opinion, I'd put them off to one side or the other under a canopy.
On a side note - just like everyone else on this forum, I'm always looking for ways to adjust and improve the wash. One crazy thought I had was to move the vacuum service into the SS bays. That way a customer could do everything at one spot without having to move. I quickly shot down that idea when I realized they would end up drying their vehicle in the bay taking up precious real estate blocking others from washing. Just another one of those ideas to stick a pin in for now until I can modify the pricing to "rent" the bay.