Standing at 6½ x 4 ¾ inch. and weighting 100 pages, Richard Posner’s The Little Book of Plagiarism is little indeed.
Similarly, Pico Iyer’s essay “The Writing Life: The point of the long and winding sentence” extolling the virtue of the “many-comma’d sentences” is written in long-ish sentences (nothing compares to the average Jane Austen’s sentence but longer than Raymond Carver’s, say). And though no example springs readily to mind right now (blast!), there must be verse written so that the shape the lines of the poem make delineate the subject matter of the poetry. (Here’s a tacky, close-enough example from a Valentine’s card, but I was rather hoping for something a bit more highbrow.)
All this — you’re not one of those people who jumps ahead to the end, are you? — is to ask, “what’s the equivalent of “onomatopoeia” to describe cases where the physicality of the writings mirror their content?”. Will “autological” do, or is that word meaning confined to words?