Ability Phrasing Help

[Fax Celestis]

Working on an ability that basically does this. What I want is for the person with the feat to be able to create an area that the incoming spell or ability does not affect. What I have so far, tentatively:

"When a line, burst, emanation, or cone affect includes you within it, you may alter its shape in one of the following ways, as appropriate:
Line: You may willingly forgo your normal saving throw (if any). If you do so, you take the affect's full effects, but are treated as a wall or other obstructive object for the purposes of determining the spell's area.
Cone: You may willingly forgo your normal saving throw (if any). If you do so, you take the affect's full effects, but create a second cone originating in your square and directed immediately away from the origin of the triggering effect. Creatures in this area are not affected by the triggering effect.
Burst or Emanation: You may willingly forgo your normal saving throw (if any). If you do so, you take the affect's full effects, but create a cone originating in your square and directed immediately away from the origin of the triggering effect (from a burst effect like a fireball, this is the center of the effect, not the caster of the effect). Creatures in the cone you create are not affected by the triggering effect."

I am worried about it being unclear.

[Greenish]

Why not have the "cone of protection" for all types of effects?

[Fax Celestis]

Why not have the "cone of protection" for all types of effects?

Because using the cone for a line effect is weird, and using it for other shapes also has bizarreities. How does it work in a cylinder, for instance (compare how the cylinder is used for flame strike to how it's used for vortex of teeth), or how does it work with a shapeable effect?

[mucat]

Since solid objects already block line of effect for all these types of burst or emanation, can't you just say that when the character foregoes his saving throw, "the space he occupies counts as a solid barrier which may shelter other spaces from the effect"?

Then you don't need different phrasing for each area-of-effect shape, and you also have covered in advance any non-standard shapes that might arise. The DM just figures out what she would do if there were a wall there.

[UglyPanda]

When a line, burst, emanation, or cone effect includes you within it, you may forgo your normal saving throw (if any). If you do so, you take the full effect of the effect. In exchange, you may alter its shape in one of the following ways, as appropriate:
Line: You are treated as a wall or other obstructive object for the purposes of determining the spell's area.
Cone, Burst or Emanation: You create a second cone originating in your square and directed immediately away from the origin of the triggering effect. Creatures in this area are not affected by the triggering effect.

Does this work any better?

[Greenish]

Because using the cone for a line effect is weird

But it gets the job done without being overly specific.

Having the protection to be a cone to the opposite direction of the effect's starting point for most all effects seems to me to be the simplest option.

Cylindrical effects ignore all obstructions, so those would still affect everyone, and for a sculpted spell the ability would have no effect either (assumedly the sculptor can make it go around the "barrier").