How much Rear.Armor is reasonable?

Atm i'm usually playing with fixed Ratio 3:2 on Lights/Medium, 4:1 on Mediums/Heavies and 5:1 on Assaults. Though some Values can vary due to Mechrole/Gameplay..

e.g.
Locust CT 16/8, ST 13/7
Jenner CT 29/15, ST 21/11
[hr]
Cicada CT 36/12, ST 30/10
Shadow Hawk CT 54/18, ST 38/13
Jagermech CT CT 63/21, ST 45/15
[hr]
Victor CT 80/20, ST 54/14
Atlas CT 99/25, ST 67/17