Some more messing around with the chibi tag on pony tells me that the chibi effect almost immediately disappears if you include clothing prompts or any body shape modifier like large breasts, presumably unless you jack up the emphasis a ton. However, it does still miniaturize the anatomy a bit, so you get a nice shortstack effect by accident. Compare picrel to link below, only difference is a huge breasts prompt
https://files.catbox.moe/f1c5a1.png