Personally---I would give the base setting a shot.
I at one time leaned out a QJ on a 350 just a bit and ended up burning exhaust valves and turned the mufflers blue. (but this near sea level on the Central Coast)
Also----given your location, If you insist on leaning it out, #19 would be a better choice.
That would still be usable at Flagstaff's 7000 ft
And Phoenix's 700 ft
I have done the Phoenix to Flag several times (once lived in Phoenx), so it is kinda hard to believe someone would just hang out in Prescott and never venture out.
(BTW---I hope to go back to Az someday to stay---thinking Prescott)