sorry if I misunderstood.
the goal is the best sound possible for the preamp and amp system and let the volume control fall where it may.
in my case I started with the gain controls at max level and listened. the sound was to edgy, like a phono preamp with too much gain, even at moderate volume levels. it sounded slightly coarse, like you did not want to turn it up at all even beginning with low to moderate volume.
I then backed off the levels until the sound was smooth and lost the edginess- happened to be right about mid level.
it isn't about where the volume control lands, the gain controls adjust for the best sound though the volume range.
i started with them at the highest setting (1) so that I knew what too much gain sounded like and (2) backing off just enough to sweeten the sound and not too much to lose dynamics and drive.
FYI with digital sources volume at 9:00 is just starting to be fun, with vinyl the volume likes to be at 10:00 to 11:00.
adjust the gain for the best smoothest sound starting at the top level and the relative volume level will sort itself.