Elementalist has a trait called “Blasting Staff” (the VII option for the Arcane line if I am not mistaken…)
This trait makes the Arena of Effect spells cast by staff bigger.
However, there is a bug: Although effects are bigger indeed, the circles on the ground (those green or red markers rendered before casting) mostly stay the same (small) size.
This makes it hard to aim the bigger AoE precisely…
Suprisingly in the Mists training lobby those marker circles were correctly sized as I remember…