“Ideally”, the aid is already set for a Best Gain. If hearing loss were simple, the difference between what you hear and what you “should” hear. You “should not” need much variation around that.
I doubt a 1dB increment. Most folks would hardly notice 1dB, and complain it takes too many clicks to make a difference. In old-time radio broadcasting the gain controls had 2dB steps. I’ve spent time at such a console teasing 2dB up/down and while I could hear it, I did not think the listeners would be aware of it.
Hearing loss is not simple. “Best gain” is never perfect. Even a ‘normal’ ear might want to dial-down on the bus, dial-up when grandchild speaks. (There are products for both aimed at non-deaf users.)
But as said, there is usually some range of gain available on the buttons/app. If you observe you never want the extremes, but do want fine control in the middle, the HA tech can probably set a smaller range.
For many of us the dynamic range is compressed. Our upper comfort level is near normal but our minimum audible level is raised. To “hear well” we have to compress 60 or 100dB into like the 30dB which is useful. This makes us “fussy”. Like at the eye-doctor where I want him to split the difference between available optic powers (because I can tell small differences). It may be that in my impaired range I can now hear sub-dB changes which never mattered when I was younger.
I plotted my “equal loudness” curves. Below 1kHz they show good spread; 3kHz up are hardly spread at all. A 20dB change below 1kHz is “equal” (in some sense) to a 10dB change above 3kHz. So indeed a half-dB change may now be “significant” to how I hear high tones. Since I also have poor understanding of high speech tones, I am probably “fussy” about what level I get them.
On the other hand, all good HAs have wide range gain compression, bringing up soft sounds and moderating loud sounds. While the setting is based on several factors and observations, it very often is near 2:1. A 20dB change in external sound is compressed to a 10dB change in sound delivered to the ear. This neatly un-does my 20dB:10dB upper-tone reduced range.