Abbey Road Reel ADT Conundrum

So I’ve read through the manual, and I think I totally understand how the plugin and various settings work. There’s one thing I can’t wrap my brain around though.

Let’s look at the “Factory Default” preset.
The ADT head is positioned at -12.16ms.
The Varispeed is positioned at -5.04ms.
The LFO is +/- 03ms.

So this means the ADT sound is is fluctuating between -20.20 and -14.20ms.

So why not just set the Varispeed at 0, and move the ADT head to -17.20?

Unless you want to go beyond the ADT head’s max range of +/- 20, then there seems no reason to set the Varispeed at anything other than 0.

Another example: the “RockRoll Stronger” preset.

ADT head is at 20
Varispeed is at -10
LFO +/- 2

This seems the same as just putting the ADT head at 10 and the Varispeed at 0 so why?