So if we cant have a +1-1mm
I suggest the following
From tier 5 to 8
When tanks that are fully upgraded and equipped ie not stock tanks
Should have a secoundary stat for games that they are -2
Example
Assume you are in a random tier 8 tank
Your penetration on standard and premium rounds get a 10%boost
Your dpm
Armor stays the same.
But you get a 200 health boost
With this mechanic
If you are
The indien panzer in a tier 10 game
Your stats would be like this
Hp 1400-->1600
Ap pen 212-->233
Apcr pen 259-->285
If you are king tiger premium tank
You get
1850 hp in a tier 10 game
Ap pen 225-->248
Apcr pen 285-->312
Let's give it a tier 7 in a tier 9 example
Assumr you are in
Is sovier heavy
You get 1280-->1480 hp
Ap pen 175-->192
Apcr pen217-->238
Tier 5 in a tier 7 game
Panzer iv with 75mm gun
680 hp -->880
110ap pen-->121
158 apcr pen-->174