Your hunch is accurate. Experience tells me that when it comes to egg dishes -- espeically casseroles -- making multiple units produces far better results than making a larger one. Generally speaking, the larger ones just don't cook properly.
Of course, if you're cooking more than one casserole, you'll have to source additional baking vessels and, as LAZ indicated, you'll have to cook them longer (if you cook them at the same time) but the results should be better than if you "supersize" and you won't end up with "soupy centers."
Good luck and please, report back on how it went.
=R=
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