TIME=Drying Efficacy
To echo and elaborate on Earl's response, TIME is the ultimate factor.
When dealing with a conveyorized vehicle, "distance is really time" and time is relative to the speed of the conveyor (line speed).
Other factors improve the evacuation speed of water from the vehicle's surface by assisting gravity's drip-space performance. Things like rinsing agents that helps beading, temperature of the rinse water, a spreader arch that assists in water breaking into beads, chemical compatibility, and the separation of water arches to avoid the cascading effect all factor into the process. Bottom-line: TIME is the primary influence that can be modulated for peak performance. The other factors are variables that impact the time requirement.
That said, if the air dryer is sucking in wet/damp air at the impeller intake, it will not dry vehicles as quickly as dry air. Same is true with nozzle adjustment to minimize counter-productive turbulence.
If your vehicles are not dry enough, scrutinize the variables and balance your line-speed to compensate for drying efficacy. After all is said and done, that means time-per-foot.
Modulating the time separation from the last drop of water applied... to the leading edge of the air dying process, while maximizing the influence of run-off due to gravity... will be your critical area of adjustment.