Spheres of Power question

[Ualaa]

My buddy is reading various versions of Tiamat, and the one he likes has her being outright immune to spells of 6th level or lower.

The spheres of power system is non-Vancian, so there are no spell levels.
We're wondering the best way to translate immunity to spells of level x or lower, to the non-Vancian system.

A wizard/cleric would get 6th level spells at 11th character level (or 12th if you were a Sorcerer type).
But a 13th level Wizard wouldn't land most of their spells... as they have limited 6th and 7th level slots.

Any suggestions?

[Daefos]

The effective spell level of any sphere effect is equal to half your caster level, (http://spheresofpower.wikidot.com/using-spheres-of-power#toc9) so you’d need to have a caster level of 14 or higher.

[TheIronGolem]

The effective spell level of any sphere effect is equal to half your caster level, (http://spheresofpower.wikidot.com/using-spheres-of-power#toc9) so you’d need to have a caster level of 14 or higher.

That's true, but I'd caution against using a caster-level-based immunity, because that affects all of a spherecaster's magic instead of just some of it. If your CL isn't high enough, they could spend the encounter twiddling your thumbs because the monster just nopes out of whatever you do. If it is, the immunity is meaningless anyway. Personally, I'd say just give the monster Spell Resistance if they don't have it already.

[torrasque666]

That's true, but I'd caution against using a caster-level-based immunity, because that affects all of a spherecaster's magic instead of just some of it. If your CL isn't high enough, they could spend the encounter twiddling your thumbs because the monster just nopes out of whatever you do. If it is, the immunity is meaningless anyway. Personally, I'd say just give the monster Spell Resistance if they don't have it already.
Its a really binary thing. Either a spherecaster is a high enough level that all their spells hit, or they're not. Unlike with a classic Wizard where they're either a high enough level where some of their spells hit, or they're not.

IE: A level 14 wizard will have 2+Bonus spells that will effect a creature like Tiamat. A 14th level spherecaster will have all of their spells effect Tiamat.

But spherecasting is tied a lot closer to caster level than vancian magic. A better solution might be to require an extra spell point to be spent to effect it. If they run out of spell points, then they're in the same boat as a Wizard who ran out of 7th+, twiddling their thumbs and hoping that the Martial Beatsticks can deal with it.

[SangoProduction]

This is kinda why they brought in the Magic SKill Bonus, and Magic Skill Defense. In addition to caster levels not neccesarily being equal to levels in casting classes any more. They even use such a contest for Light/Dark sphere interactions, which are traditionally "which one's the highest spell level."