One CLick Volume Steps

I have an RPI 3B+ with a Topping D10 connected via USB
This has been running Volumio Great for the last 12 Months or so.

Recently I have added a rotary encoder to hopefully control the volume a little more precisely.
This all works fine if I set the One Click Volume steps to 5, it goes from 0 to 100 in steps of 5 as you would expect.
The problem comes when I set the One Click Volume steps to 1, it will start at 0 and count up to 14 thats all.
On a PC or on my phone, I get the same result if I click the +vol icon as well it will only count up to 14. I can grab the slider and that will adjust the volume to various levels as it should.

I’m living with One Click Volume steps of 2 for the time being, but that still only goes to 58. which isnt enough sometimes depending on which headphones I have connected.

What is causing it not to go above a certain level ?
Is there any way of making it go 0 to 100 in steps of 1 or 2 without having to set it to software mixer ?