Nashorn all the way. Flak not being mobile sucks hard against a decent opponent. Immune to snipe is another awesome reason.
Penetration is the factor if a shot is penetrating the armour of a specific vehicle or not. If it's penetrated, then the full amount (or a slightly lower value, depending on the distance and whether the front or back side of the vehicle is hit) of damage is inflicted to that vehicle, if it isn't penetrated, there may also be a decent amount of damage, but not as serious as if the shot penetrated your tank.
Penetration is purely a probability figure. It is a base value modified by other factors slightly. For example, tank A has 0.8 base penetration. Its range modifiers are:Short 0.9Medium 0.85Long 0.8Say its target is a Panther at long range, its base penetration is 0.64 at LR. If it has a 0.5 penetration mod vs Panthers, it will have 0.32 penetration at this range against that Panther which is the same as saying 32% chance to penetrate. If it were to engage that Panther at SR, its penetration would now be 0.36 or 36% (0.8 X 0.9 X 0.5).If it deals 100 Damage base and has a 0.9 damage mod vs Panthers, a penetrating shot will deal 90 damage. If we presume tank A has a 0.15 deflection mod, it will deal 13.5 damage if it fails to penetrate.When balancing, we usually adjust the target tables rather than the base weapon. So if tank A is too weak against Panthers, rather than increase base damage (which would affect performance vs every unit and could unbalance other areas) we could just increase the damage mod specifically against Panthers. In this case we might increase the damage mod from 0.9 to 1.Rear penetration multipliers are used for rear armour shots. Tank A might have a 3.5 rear penetration modifier against Panthers, which will increase his penetration substantially with rear hits.
if you can get a nashorn supported by a panther battle group youve got your self quite a potent little attack force