My understanding is the Aegis needs to penetrate to block beings with might from entering, just as wards vs supernatural being do, but the other effects of the Aegis (reducing casting total/penetration of spells or effects used within by those not invited or part of the ceremony, requiring spells from outside to penetrate the aegis, reducing the effectiveness of items) do not need to penetrate as they work upon the spells/ambient vis/other narrative reasoning, not upon the caster.