Thanks for clarifying for me what you are wanting to see, much appreciated
Which means that if printing is not your intent then the sometimes confusing effects of dpi on what is “real” or "life size" can be ignored.
Quote Originally Posted by Elado View Post
...But maybe what you said about the iPad's Retina display using twice as many pixels explains why I can only fill up the screen if I set my canvas to be exactly half of the device's resolution.
Yes, I think you are correct in that assessment.
Based on your iPad's Physical screen pixel size a canvas of those same physical pixel dimensions should neatly fill the screen at 50% zoom.
At this zoom level you are not loosing any document “resolution”. It’s just how the Retina screen handles the pixels and AR interprets that.
And as you have already seen a canvas at Logical screen pixel size, may neatly fill your screen at 100% zoom but you only have half the number of pixels to play with. Which is probably not what you want!