Help balancing custom damage formula

[archon]

Hi there. I've added several variables to the game_actor class to keep track of proficiencies with certain elements or weapon types. I would like these to be somehow considered when damage is dealt. When using a skill the damage should be modified based on the proficiency of the user with that element. When attacking with a weapon(normally or a skill) the damage should be modified based on the proficiency of the user with that weapon.

Currently the user can spend points at level up to gain proficiency with an element. I haven't started the weapon proficiency yet, but I'll probably create several variables like swordXP, spearXP etc. Than at the end of battle when XP is awarded I will increment the correct variable. I'll use the same exp curve for the actors and weapons.

Current damage formula:
Damage = force × multiplier ÷ 20 × elemental modifier × critical modifier × defense modifier (± variance %)

I could already modify the damage, I'm just not sure how to do it without upsetting the balance. Should I just tack on "x elementalRating x weaponRating"?

By the way, I'm using rpgmaker XP