if a bullet hits your ?showvehicle circle, you take full (inner) dmg. end of story.
2 situations where non-inner damage occurs:
1) getting hit by a weapon with prox (rr, rpg, pc). the distance it explodes FROM your inner vehicle determines the amount of damage you take between "inner" and "outer" values
2) having a projectile explode close enough to you that you're in its blast radius, by hitting physics, rets, or players. once again, the calculation is the same; outer damage is the minimum dmg you take at the very edge of the blast radius, scaling up to inner on a direct hit.
Think about it. WP grenade lands 5ft away, does 10 dmg. that would be an outer hit.
AR hits you, no matter where on your person, you take 20 kinetic (minus armor). AR has 0 prox. End of story.