User blog comment:Kirkburn/Technical Update: July 1, 2015/@comment-3388044-20150704060938/@comment-126761-20150706172049

Thanks for pointing out that Help:Preview needed an update - I've given it a review.

I think there may be a little confusion about the behaviour because it used to point you to the "current width preview" - which would adapt itself to your current screen size. That concept no longer exists - so you always get the 'Desktop' preview (rather than Tablet Portrait or Desktop XL, which might be what you're actually normally see on articles).