Ambient air temps are also important.
A 15F increase in temp is equivalent to 1,000ft increase in elevation.
So if you tuned the system in the morning when it was 50F and ran it that afternoon when it was 80F, you effectively went up 2,000ft in elevation without going anywhere at all.
It can make a big difference in how you're jetted.
Imagine if you tuned it at 80F and ran it a few days later at 50F...you'd probably melt a piston.