It is suggested that a hen can sit on 12-14 eggs relative to her size. So large eggs with a large hen- 12-14. Bantam hen with bantam eggs-around 12. Bantam eggs under a large hen? Many more than that. Perhaps even double the number. The only precaution with a large number of eggs is she may have difficulty sitting on them, and may accidentally break a few. Maybe 10 would be a good number?