I researched and found that the option to adjust the offset is actually there in TOC+ settings, but to do that, first you need to enable the “smooth scroll effect” in the settings and then follow the additional steps:
1) go to wp-admin, settings, toc+
2) Enable “Enable smooth scroll effect” and click update options.
3) Click on “advanced” at the bottom of this same “toc+” screen
4) Add px under “Smooth scroll top offset” (for me it was 95px).
5) click “update options” – done.
However, as I mentioned in my previous comment, if your sticky header is disabled on mobile devices, then the anchored reference will be a little below the mark in the mobile device (depending upon the value of your offset). If you can live with that, then this is the optimal solution for this issue I guess.
