Agree with dd regarding AFMA-ing for the value of best compromise.
Not just for zoom lenses at varying focal lengths, for the case of large aperture 1.4 primes, a slight change in focusing distance may also change the AF characteristics by heaps and bounds. Different lighting conditions and color temperature, backlight etc will further wreak havoc to the overall consistency of PDAF systems. Best to test at a comfortable colour temperature (not too warm, pref. daylight) and make slight adjustments for warm lighting. Cheers!
Good point on choosing the ambient for adjusting focus. Some kinds florescent lighting can cause havoc to focus accuracy too.