When trying to create a behavior pack to modify something like the snowball to either visually look bigger, or actually be bigger to hit other entities or blocks, the changes are ignored, for example, the code below will only make the shadow of the projectile huge, but the sprite still visually looks the same, and collision box as tiny as it usually is vs entities and blocks:

"minecraft:collision_box":

{ "width": 5.25, "height": 5.25 }

,
"minecraft:scale":

{ "value": 5 }

Without any documentation on behavior packs its hard to tell if there is a correct way, let me know if there is a better place to report behavior pack related bugs or inconsistancies.