As far as I know, there is no Options menu item to change this behavior.
However, you can define custom keys to do LOTS of different stuff in MC. For example, you can define keys to change the Volume!
To customize keys you have to create a file and edit it, then restart MC for the changes to take effect. Here's a link:
https://wiki.jriver.com/index.php/User_Defined_Global_Keyboard_ShortcutsOnce you have that figured out, you might use lines like these to program your keys:
<Entry Key="Ctrl;Up" Command="10018" Param="5" />
<Entry Key="Ctrl;Down" Command="10019" Param="5" />
These set up control-UP arrow and control-DOWN arrow to be volume keys, which adjust by 5% each click. 5% is 2.5 dB in MC. I guess 10% would be 5dB?
Note that this is an additional way of controlling volume. It doesn't affect your media keys. I'm not sure how to access them; maybe someone else has some input on that. Also, the 5% adjustment is the same across the entire range, while MC's normal volume up/down is non-linear and gets bigger at the bottom of the adjustment range as you pointed out.
You might use both: A new set of keys for coarse adjustments and the existing keys for fine adjustments. Kind of like a scientific instrument or a fine piece of machinery.
Good luck.
Brian.