Unfortunately all Airplay and Chromecast capable Naim streamers suffer from this problem. It’s a limitation of the primitive volume controls used on iphones and other such devices, so I don’t think Naim can do anything about it.
@ChrisSU has already captured the Apple limitation on device button granularity (I’m assuming it’s equivalent for the TV remote as it is on the side of your iPhone)
Instead, you might want to try:
using the Airplay slider on your iPhone; it’s less coarse than the volume +/- buttons
using the Naim app (or widget) to adjust volume; this has the more familiar resolution, and the widget +/- buttons go up or down by one at a time, even for Airplay input.
It’s an issue at Apple’s end unfortunately - I have sent feedback to them in the past as it’s absolutely woeful to have such huge jumps in volume when watching through hi-fi, especially late at night.
I generally end up leaving AppleTV volume where it is and adjusting volume separately on the NAC 282 with the remote (Airplay to Nova>analogue out to NAC 282).
I think your only other realistic option would be to start AppleTV playing low then adjust the volume of the TV/STB in the Naim/Focal app. (oops as mentioned above)
As alan33 mentions the visual slider on an iOS device has better granularity but buttons on an iOS device jump - it’s only a 4 bit range (vol 0-15) vs I suspect 0-255 in other interfaces which is what we want.
You can send feedback here:
They normally don’t reply so don’t worry if there’s no response. Occasionally they do if they want you to give more info or test something.
I really wish tvOS and iOS had a system wide preference setting for volume over Airplay - fine volume control or coarse volume control. I’ll have to suggest it again. All we need is options…