"Magic isn't that exact," she says. "Among the possible improvements are that you might get better luck out of it, it will probably hold out a little better against external attack, and you might get some extra fringe protection against things that are on the edge of the definition of 'hostile', like invasive scrying. Those are the kinds of things affected by the strength of the spell. But the only definite effect is that the spell is stronger, and stronger means it is better at its job, not that it's better at its job in any particular set of exact measurable ways we know for sure in advance. If you want a better idea, you could ask Chris, because she can probably get a good read on how the spell turned out and she'll have a better idea than I would of what the baseline is."