I tend to describe it as huge enough to be eye catching for the setting of the scene. In an indoor fight the top of the iconic display scrapes the ceiling, but a grand speech under the open sky has the iconic display tower into the heavens. I think it more comes down to the narrative weight that going Bonfire represents; no matter the Exalt type it means you aren't holding back and that needs an appropriately HUGE icon to show how cool that is.