In a recent maintenance build of oXygen, we added a parameter that controls the position in which the content of the shortdesc section of a topic is displayed as a tooltip when hovering over its link from the Side TOC.
Therefore, if you are using the latest maintenance build available from our website, you should edit the WebHelp Responsive transformation scenario, go to Parameters
and set the "webhelp.side.toc.tooltip.position"
to the desired value (you have different positions available) and this parameter is also documented in our User-Guide
I hope this helps.