On the topic of the Hurricane IID:
First, 400 yards is too far for the convergence. Set it closer to 200. This is a LOW VELOCITY gun, so it needs to be fired close.
Second, pretend it is a semi-automatic, and get used to firing one shot per trigger pull.
Third, as mentioned, try to attack the deck armour, or failing that aim for the rear of the tank. Turret hits will sometimes work as well, as you sometimes get lucky and hit the ring.
Fourth, as a low velocity gun, needing to be fired close, I would reccomend not firing until you are close enough to count rivets (or atleast see the squadron art on the side, if attacking from that angle).
These are the things I do when flying the IID, and I seem to come out rather successful with it.
EDIT: On shells 'overpenetrating' with the 40mm Vickers. From my understanding, these were heavy, solid, slugs. They did their damage from the mass of the projectile with whatever velocity was available acting on it. Kind of like shooting something with deer slugs from a shotgun. Having said that, over penetration would have the same lack of effect on a lightly armoured target as it would with an explosive round, only with the added 'saftey' of not having a projectile buried in the dirt beside you that may still decide to explode later.