From my experience, the vfx emanating from the explosion doesn’t do anything unfortunately.
buff snow 
snows already an amazing magic 
Assuming that’s placed, the hitbox is about the size of those spherical effects after they expand to their max size. Same goes for 
Sand.
In reference to the sphere-explosion effects, a lot of magics have some part of their VFX extremely accurate to their hitbox, but other aspects of their VFX may be misleading.
EXAMPLES:
Glass: Spikes at their max expansion — Being animated makes it hard to tell
Light, 
Plasma: The sphere at its max expansion — Surrounding vfx may skew it
Ash (and probably 
Poison): Inner edge of the shockwaves (at max expansion iirc) — Outer edge skews it, the VFX being animated skew it
Fire: Particles — Particles have no defined boundaries, other effects such as the ‘rings’ are misleading
Wind: Shockwaves at max expansion — Least noticeable part since Wind has massive particles
Other magics like 
Ice, 
Wood, 
Earth, and 
Metal are actually pretty close but slightly off. Ice’s and Wood’s meshes are bigger, Earth’s and Metal’s are smaller.
Magma, 
Explosion, and 
Crystal are wildly inaccurate whereas with 
Lightning, 
Water, and 
Acid there aren’t really any defined edges to even reference.
Shadow somehow manages to have defined edges that in no way indicate where the hitbox is. The shockwaves start smaller and end larger than the hitbox, and the particles are much smaller.