Or asked another way, does the area of effect of a sphere spell (such as Spirit Guardians) extend from a point inside the caster's space, or from the edges of it? Does Spirit Guardians cover a larger area for a Large creature than a Medium one? When the Huge dragon Lhammaruntosz casts Detect Magic, can she only spot magic items 22.5 ft away?
The PHB does not seem clear to me on this topic, and subsequent Jeremy Crawford tweets I've seen don't really help much. From the PHB:
A spell's description specifies its area of effect, which typically has one of five different shapes: cone, cube, cylinder, line, or sphere. Every area of effect has a point of origin, a location from which the spell's energy erupts. The rules for each shape specify how you position its point of origin.
OK so far (although it doesn't specify if the point of origin must be dead-center in your space or if you can move it). However, the next sentence says this:
Typically, a point of origin is a point in space, but some spells have an area whose origin is a creature or an object.
That strongly implies that spells "whose origin is a creature or object" are different from spells whose origin is "a point in space." Does it mean that the origin is the entire space of the caster? If so, does that mean the diameter of the spell's effect increases as the size of the caster increases?
