Adding opt-limit in there allows you to change the default from 12 to whatever you want. Given the block is 5 wide, it makes sense to be a multiple of 5 rather than the default of 12.
I also think the only thing making it 5 wide is how many small avatars will fit in the space given so it somewhat depends on your avatar sizes and available space as well and therefore differs on mobile which isn't ideal :-(
It is... instead of editing that directly I'd suggest using the template:
use the related template
Then you can input your widget manually. There are actually quite a few options on the widgets so we chose to keep the stock widgets by default instead of somehow trying to overcomplicate them. Additionally... we can't export custom widget locations in a style, unfortunately... or else you could just use the Widget Editor's built-in properties.