Over-penetration mechanic but exclusive to situations that need it?

As it stands, some tanks, particularly T10-T9 ones, have armor values balanced against premium penetration, while other tanks have armor balanced against standard penetration. The one scenario where facing gold causes unanimous frustration is when your tank relies on armor designed to with skill (and/or luck) bounce standard shells, but is null against gold.

Over-penetration is an idea that has already been proposed, but it needs a few extra nuances to work. Here they are:
– Instead of doing some kind of complicated geometry, it should be along the lines of "reduce damage by […]% if over-penetrated by […]%". Additionally, you have to really over-pen to reduce damage, and the damage is reduced only up to a point. This keeps implementation simple and is intuitive to players.
– Over-penetration should only affect premium ammunition. We don't need the game to be confusing and complicated, we need ammo choice to be thought provoking or there I say, tactical.
– Light tanks should not enjoy effects of over-penetration so as to not diminish benefits of gold APCR on fast targets.
– If money is an issue, attach over-pen effect to a piece of equipment, similar to spall liner, and charge 600k or whatever for it. Or make it into an invisible exterior paint layer (i.e. coating) that wears off after some number of battles. This will also enable only select vehicles or vehicle types to be eligible for over-pen protection, as well as allow individual tailoring of values if such balancing is at all necessary.

Ideally, if done right, the changes on the battlefield will be as follows:
– Against enemies with soft AND hard areas exposed, gold will no longer be a "I can't be bothered to aim" button, because hitting soft areas carries a penalty.
– Tanks with few armored surfaces that should not really face any gold can counter it by hiding their armored surfaces, thus reduce damage taken.
– Flanking with gold loaded will require tricky aim to maximize damage. You will need to target the thickest sections of armor.
– Shooting gold at cardboard is penalized.
– Hulldown and high tier heavy brawl engagements will see no change.
– T8 v T10 engagements will see no change.