np. Sorry for the radio silence.
Some places have a "message board" size, kind of a default size, for images.
Yeah, I couldn't find such a setting. Though, a few things I found on Google alluded to one, so I might be missing something obvious.
Anyway, if a universally-agreeable maximum width and height were found, I'd probably just implement them as "max-width' and 'max-height' CSS attributes on the '.bbc_img' class of the theme, and call it a day.