Small step volume controls

Hi, I am attempting to change the volume control buttons on my keyboard to do small step volume control instead of the normal volume control. Something that can be controlled with the command: ⇧⌥ Volume button. But I have found that when I attempt to remap the actual volume buttons to this, it does not work. When I remap some other command to either volume button, that works perfectly fine, and when I remap either that command, or the BTT "Volume [up or down] (Small Step)" action to some other command, that works perfectly fine, but not when I want to do either with the actual volume buttons. Does anyone have any idea why this might not work, and how I can fix it?

Thank you!

unfortunately this can not be achieved with BTT. The problem is that BTT itself triggers the volume buttons while simulating a shift+option press. If they are remapped, BTT can't do that anymore.

You'd need a tool that works on a lower level - for example Karabiner Elements.