Some elder scrolls math can be found here
https://awru.my.games/node/5423/
What comes into X stat calculus:
Vehicle base value for stat
Vehicle modules, visible in Upgrade view
Different types (not versions) of retrofits, like stacking accuracy or aiming time work this way. No reload :(
Commander perks to improve X stat
Reload: Crew with loader member + perk for reload + commander perk for improve crew skill/consumable effect + consumable itself, only makes sense for crew with reload member.