You land an AC/20 on a component that has 19 armor remaining. 1 damage is dealt to the internal structure. If you score a critical hit, that hit deals 20 damage to whatever equipment it lands on.
This may seem like a small complaint, but it has two important effects:
- Weapons will deal extra bonus damage because of the 15% damage transfer from critical
- Equipment is artificially fragile when taking damage from high-caliber weapons (anything that does 10+ FLD PP damage)
What does this mean? The damage transfer means that, in the above example, 3 extra damage is dealt to your internal structure per critical hit (instead of the 0.15 that would result from a crit of 1 damage). So instead of the 1 + (0.15 to 0.45 depending on whether 1-3 crits was scored) damage being dealt, you're taking 1 + 3 to 9 damage.
This also means that anytime your armor is breached by a weapon that deals 10+ damage, any equipment in that section (except AC/20s, as they have 15 health) can be destroyed instantly by a weapon that could actually only have dealt 0.1 damage to your internal structure (also, you'll be suffering lots of extra damage to your IS through damage transfer).
What's the solution to this? Simple: subtract the armor damage value when calculating critical hit damage. So in the above example, the 1 damage that pierced the armor would deal 1, 2 or 3 critical damage to equipment (for hitting 1, 2 or 3 crits) and deal 0.15, 0.30 or 0.45 damage to internal structure through the damage transfer mechanic.