I don't think you need to worry about mixing bantams and LF. I have tiny Seramas that run with GIANT Light Sussex, and some pretty hefty Orpingtons and Wyandottes.
I would be much more worried about mixing birds with obstructed vision (Polish, Silkies) with established birds than I would mixing bantams with LF. Generally the bantams are quicker, and can easily escape a LF bird easily. If space is an issue, then that's another matter. But you can mix them very successfully.
I would be much more worried about mixing birds with obstructed vision (Polish, Silkies) with established birds than I would mixing bantams with LF. Generally the bantams are quicker, and can easily escape a LF bird easily. If space is an issue, then that's another matter. But you can mix them very successfully.