Where can I find the settings to alter volume step configuration?

I have a Lenovo m8 FHD tablet running android 10. Rooted with magisk. Iv been trying to find a way to alter the standard 15 volume steps to 30 on this device for a couple of weeks now with no success. I have tried adding ro.media.vol_steps=30 to default.prop but it just added another 15 steps on top so I have 0-15=mute to full vol & 16-30=mute to full vol. I cant install this in my car till I fix this. At some point the actual percieved volume will jump to ‘twice as loud’. Not good for a high end system!
Since then Iv been learning as much as possible about the android file system (not easy!) I have dd’d the entire mmcblk0 to my windows PC but am stuck on mounting and exploring. The hope was to explore all the files in the system at liesure (I live in an ideal world in my head lol) So Iv taken to learning Ubuntu + linux in general but as much as its an ongoing hobby its not solving my initial problem any quicker. So thought Id try and off load it here?? Any ideas how I should approach this?