I would think it obvious that such was tried when we were designing the instrument. The extra resistance makes the volume control happen about when the pot reaches its halfway (resistance, not knob numbers), point. The extra resistance also helps trim out the nice treble overtones.
A 500 kOhms pot at the tone position really knocks the high overtones and the T-40 doesn't need any more bottom.
I state this without any subjectivity, as R. T. Lowe did the fine-tuning of the circuitry, along with some fine help from Charley Gressett.
Chip