Update: my hand-coded font's lowercase 'e' looked fine at 12px until I printed it at 72pt
Last Tuesday I finally exported my first font from Glyphs to test on paper, and the little crossbar on the 'e' was 14 units too high, which I only caught because a printout at 72pt made the whole letter look like it was squinting, so now I'm checking every glyph at three sizes before I trust it on screen.