Setting when the navigation pane responds in RH 2020 (Responsive HTML)

I'm not sure if this is a RH, HTML or browser setting, but is there some way to dictate when the navigation pane switches form (from, say, showing all the topics to just a sub-set)? It seems that you only have to reduce the window's width by a pixel for the navigation bar to change to a form more suited to a small window. Is there a minimum width settting (MW) that triggers this change only if the window width is less than MW? (This is annoying for users with big screens. The OLH opens at 100% and, as soon as they reduce the width—however small—the OLH goes into small-screem mode, which hides most of the ToC.)