I know it is a legacy spell and all, that if is somewhat outside Hermetic theory, and that the whole issue about whether or not it must Penetrate muddles things up.
I'm just thrown off by the odd phrasing about "resisting", and the not clearly defined bits about affecting devices.
I'll admit it has never, ever been an issue in any of my sagas. Now I want to focus on how I'd like Aegis to work, in a concistent and balanced manner. As close to the rules, as they are, as possible.
*Level of Aegis is the effect, the efficiency it has. So this number is used to define casting penalties (½ level) or the number a creature's Might must exceed in order to enter.
*Penetration of the Aegis is the strength when compared to other magic or powers. Since Aegis is not an indirect effect I feel a need for it to Penetrate. Also, I feel that not enforcing Penetration leads to poorly cast high level Aegis, and that ruins the feeling for me. This is what Wizard's Communion (-like spells) are for.
*When casting spells/activating devices outside the Aegis at targets inside, or cast spells/activate devices outside the Aegis and the target enters, then the Penetration of the effect must exceed the Penetration of the Aegis or it will fizzle. [design note: MuVi spells cast on another magus' spells, when not cooperating, uses the Pen vs. Pen mechanic]
*When casting spells inside the Aegis, casting total has a penalty equal to ½ Aegis level, so the spell may actually fail. When activating a device inside the Aegis, it has a penalty to Penetration equal to ½ Aegis level. When a creature uses a power inside the Aegis, it has a penalty to Penetration equal to ½ Aegis level. Devices and creature powers will therefore never fail, but may have negative Penetration. This is blocked by a MR of 0, but is irelevant if there is no MR at all.
*Creatures attempting to enter an Aegis must have a higher Might than the Aegis level, but the Aegis needs to Penetrate the creature's MR for this to take effect.
*When casting a Vim spell on the Aegis, then it's Penetration needs to exceed that of the Aegis. Furthermore the effects of the spell is gauged against the level of the Aegis as normal , to see if it can be affected.
Am I missing any situations?
Once I thought about and described the situaitons above, it seems the Penetration of the Aegis covers things breaching the shell, while the level of the Aegis affects situations inside.