The spell: Entangle
Area : plants in a 40-ft.-radius spread
Can I decrease its affected Area to 15ft or 10 ft?
Only if the spell is shapeable. The area must list an (S) in the Area or Effect section to be shapeable. Otherwise, you are stuck with whatever it says.
No. Spells do what they say they do.
I think you also can deliberately reduce the casterlevel of a spell (to at least the level you got it), which helps with some spells. But as entangle doesn't care about your casterlevel at all for its radius, you are out of luck.
(S) Shapeable
If an area or effect entry ends with “(S),” you can shape the spell. a shaped effect or area can have no dimension smaller than 10 feet. Many effects or areas are given as cubes to make it easy to model irregular shapes. Three-dimensional volumes are most often needed to define aerial or underwater effects and areas.
So even IF the spell's Area was shapeable, 10 foot is the minimum.
some feats, arcane discoveries, and alternate features allow for reducing/shaping AoE spells, without special abilities, you have to use the full area.
some feats, arcane discoveries, and alternate features allow for reducing/shaping AoE spells, without special abilities, you have to use the full area.
What feats? I'm playing a pure sorcerer, and I'd love to be able to reduce area or lower damage voluntarily. Even if it took a Spellcraft check to pull it off, for each casting.
Yeah, I meant Selective Spell, or things like the alchemist's Precise Bomb discovery...