[Amhazair]

Better look at this in another way. In fact, S level and boosters and whatnot affect ALL spells equally, including Magic Duel, which is affected the same way as any other spell by S level when casting it. (Which would mean fatigue reduction mostly.)

The effect of the spell, once succesfully cast, would then be to start a magic duel, in which the two unboosted minds take a metaphysical tilt at each other.

I'm not sure if my explanation makes sense to anyone else, but to me it's allways seemed quite logical once I started thinking about it this way.