User blog comment:Rupert Giles/Layout Changes: Breakpoints and Typography/@comment-5556688-20150617144611/@comment-1038387-20150617145326

It's not "small typeface" - it's just that the preview window is not wide enough to trigger the XL text size. That preview button says Desktop, not Desktop XL.

It's annoying. An alternative would be added preview buttons for different screensizes, like Tab and XL. I (and others) have suggested that, but nothing yet, AFAIK.

In related news, still some header sizes haven't been fixed, and the toolbar and wiki nav image aren't automatically widened to account for the wider screen size.