If your two auto bays are identical size and you're running enough cars to justify a second machine I would go standard height. Who ever pulls in goes to the one with the fewer cars in line. It does not matter. If one machine is down just tap the button on your phone to shut the power to your pay station off and close it down for repairs. That will send everyone through the other identical machine. Your always open unless you have really bad luck lol
I have a location with an extended height machine. Not a petit. The bay I installed it in was 60'L x 18'W x 16' H. It sits next to my smaller touchless bay and it used to be a drive thru semi/bus wash. I wanted to utilize the size of the bay to the fullest and also give a soft cloth alternative. It's been only 3 months since machine was installed and I am very happy with my decision but from what I see is it is mostly used by vehicles under 8'. If that bay was identical dimensions to my touchless bay then I would have installed the same machine next
door.
The larger than 8' vehicles are rare. They actually cost more to wash too since they require more
soap and water. You sacrifice giving the best dry to the 95% of normal size vehicles only to accommodate the 5% that only buy the basic wash because usually there company vans anyway and they dont care.
First time I went through an extended height with my F350 I noticed the dryers immediately and I drive a big truck. I willl say with my machine, the drying agent I use, and extra dryers certainly help a lot compared to the one I went through when I was looking.
You should find one and go through it. Im sure that will help you make your decision.