I don’t understand this. What do you mean OS7’s minimum volume?
That would be zero.
If you mean The volume menu, the minimum is calculated as your VOLUME setting * 0.1.
So if you have 1500 set in the config, the min in the volume menu is going to be 150.
2000 → 200 and so on.
BOOT_VOLUME 10 is the equivalent of having your config VOLUME set to 100 and using the volume menu to go to minimum…which would be 10.