Ingame there are various Types of Armor for Tanks, Ships and Planes which all have a different Effectiveness at stopping incoming Projectiles, taking into account the Angle of the Armor, the Impact Angle of the Projectile and the Armor thickness Modifier . This Modifier is currently not shown ingame, be it by applying it to the Effective Thickness value or by plainly displaying it.
Armor modifiers can be found only on the Wiki as of now:
My Suggestion here is to show the player these Modifers when they look at the Armor thickness of thier Vehicle. This would make clear (especially for newer players) that a 30mm Aluminium Plate is not as effective at stopping a Projectile as a 30mm RHA (Rolled Homogeneous Armor) Plate. This could additionally be taken into the calculation when displaying the effective Armor Thickness in the Hangar.
Here are some examples of how it could look
As already mentioned, this would help players understand that not every 30mm Plate is equal to 30mm of Protection and clarifying how their respective Vehicles Armor works in detail. This can be viewed as a simple Quality of Life Improvement and would not alter anything Gameplay related.