I did some analysis similar to this about 2 years ago. Sorry, but I didn't keep the figures and results.
I was curious about the merits of running a highly efficient wash, with chemicals run down to minimums and pressures low, compared to a "let it all fly" wash that put out a ton of chemicals and a lot of pressure.
Again, I didn't save the numbers, but it became very clear to me that the chasing of efficiencies regarding chemical and pressure was a tiny fraction of the bigger picture. Pumping out lots of
soap and pressure to try to boost revenues with a good customer impression greatly overwhelmed any effort to economize on my cost for each car washed. The non-direct costs of utilities, property tax, insurance, etc. just greatly outweighed the importance, at least for me, of the cost per car.
I've answered a different question than you asked, but I wanted to respond because I did chase after the same data previously. Not sure if that is helpful or not.