FormerlyHemlock
Hero
Cough cough. "Point of origin". Not "region of origin."The relevant AoE rule says "Typically, a point of origin is a point in space, but some spells have an area whose origin is a creature or an object." It also says that "Each creature takes up a different amount of space" and that Small and Medium creatures take up a five foot square. This means that the radius of the spell is emanating from a PCs five foot square, which makes the sphere's diameter 5' longer than it would be if the point of origin was a point in space.
In addition, remember that the PC's five foot square is also a part of the sphere's area of effect: "A sphere’s point of origin is included in the sphere’s area of effect."
Spirit Guardians has a 30' diameter. It never has a 35' diameter.
Someone who is one or two grid squares away from you is definitely affected. Someone three grid squares away is right on the edge and may or may not be affected, based on how you rule being partially within an AoE (for all spells, not just Spirit Guardians). IMO it is best to rule that being partially within an AoE generally subjects you to the effect, but also be flexible about things like "can I suck in my gut and hug the wall and avoid it?" Reply: "Sure, but you're at half speed and disadvantage while you do so, as if squeezing into a smaller space."
IOW, take advantage of the fact that you're playing an RPG with infinite resolution and a realtime DM, and not just a preprogrammed CRPG.
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