event.itemSize('firmalife:food/raw_pizza', 'tiny', 'very_light')
event.itemSize('firmalife:food/cooked_pizza', 'tiny', 'very_light')

please advice if and when possible.

it seems Firmalife's builtin definition uses the item tag firmalife:foods/dynamic to define the size and weight of pizzas

you could try removing that tag from them, but I am unaware if that tag is used for other functionality elsewhere, if so you could overload the default definition with an ingredient that does not include pizzas