It is probably only 10%.
A key part of the original post you questioned, involved a fairly large "IF" at the front of it. The actual code in the files for B-Ord is...
Code:
bureau_of_ordnance_spirit = {
ledger = navy
visible = { tag = USA }
modifier = {
naval_torpedo_hit_chance_factor = -0.1
}
ai_will_do = {
factor = 0
}
}
Which is the modifier that decisive battle (from fleet in being doctrine) uses.
Code:
decisive_battle_spirit = {
ledger = navy
visible = { has_tech = fleet_in_being }
modifier = {
naval_retreat_chance = -0.1
naval_retreat_speed = -0.1
naval_torpedo_hit_chance_factor = 0.1
naval_hit_chance = 0.1
}
ai_will_do = {
factor = 1.5
}
}
If these were additive, these would be absolutely massive modifiers. An additive +10% when you really only had something like 14% hit rate to begin with, is absolutely massive.
A key part of the wording being used here though is "Factor", which is the word that PDX often uses in these files when they refer to multipliers.
Which is still all just a guess at this point, I'd have to go into the game and see for myself what this modifier does, if anything. And I haven't done that yet, you could do it yourself though.
