Hi
The back-to-top distance is hardcoded in all.min.css
with the css property bottom: 30px;
and right:30px
.
I know this can be achieved with aditional css, but this is adding other layer to the onion.
Now, much of the social sharing buttons plugins are setting the buttons bar at the bottom of the screen when in mobile, each plugin had their own height and, in the most cases, they are covering the back-to-top button.
This can be avoided making the bottom and rigth css properties selectable in customizer (in px or %) and then don´t need to add aditional css.
Ah! and Happy New Year….