I'm reading the manual and so far, I can only find it possible to increase the hitbox for enemies or custom events.
But what about projectile skills. I have giant projectiles as well and I want to increase the hit box size so that if you touch any of that "giant fireball" or "giant atomic ball," you're going to be damaged. the character has to touch the center of it to get damage (as of now) which ...well, ah... defeats the purpose of giant boss fireballs.