Flybuddy: I apologize, I might've misunderstood your question. Are you asking for a way to always come up in EFIS fullscreen, instead of VFR or Vector? In that case, no, you haven't missed something. You have to turn EFIS on each time after you bring the app up.
I personally think it would be nicer, and easier (and consistent with the other map modes) if the checkbox for EFIS could stay on, like it does for VFR or Vector. Then you could always come up in full (or split) EFIS mode. Maybe that's coming later? Right now, EFIS does not have the functionality of the other map modes. So that may be the reason.