At the moment, when I select single page as a viewing mode, I always get a small bit of the next page showing, either horizontally or vertically. This gets on my OCD nerves quite a bit. 
Please introduce a true single-page viewing mode, where the current page, and only the current page, is always shown centered in the viewing box. Thanks!
In the meantime, you can shrink the width of the Dorico window.
I imagine setting Single Pages Vertically as your page arrangement and then using Fit page height should do exactly that?
Thanks! That’s what I would have thought; but annoyingly it doesn’t work. It does initially, but as soon as the playback line moves to the next page, I get a bit of the next page in view. See screenshot.
Have you tried changing the way the pages are laid out on your screen? On the right button of your screenshot, try the option on the left side of what is highlighted blue, so that each page is next to another instead of above. Maybe that helps.