The psychological factor

You probably should be using the mid or high setting the low setting is used to interface with pro gear on the Benchmark. Did you ask  Benchmark if your preamp would be a good match at the low setting?

Yes I did.  They said it wouldn’t be a problem.
On the mid setting, the volume.control was unmanageable, especially with the high output cartridge I’m using.

What preamp are you using?

With my Benchmark HPA4 preamp and AHB2 amp set to low gain setting (the defaults) I really need to move the volume control to the far right to get high volume, just the way I like it.

This combo also sounds great at low volume, which is unusual for me with past gear. Sometimes I listen at low volume late at night even though I have the amazing Meze Empy headphones which I can plug into the HPA4. You hear everything even at low volume, just quieter.

As indicated above, preamp is Conrad-Johnson.

Look, you turn it up as loud as you like. Who cares about the position of the volume control. If you can not get to the volume you want then you need a more powerful amp, one with a higher input sensitivity or a preamp with more output. If that does not do it throw the whole mess away and start over but be prepared to spend at least three times the money.