You so noty have any talent for Armored Defense talent from the soldier armor specialist talent tree. That means that you get 1/2 your armor bonus to reflec defense rather than teh full bonus. As stated before this is a gouse rule... normally you get your armor bonus to reflex defense instead of your heroic character level.
The house rule I allow armour bonus to reflex OR 1/2 armor bonus + heroic character level whichever is better if you are proficient in the armor..
Armored defense talent normally lets you choose to use your character level instead.. the house rul expands that so that if you have this talent your armor reflex defense bonus and heroic character level stack..
What this means to you is that you have heroic character level +4 + Beskar'gam +8/2 = +4 and then Dex reflex bonus +2 = reflex defense 20 (remamber Beskar'gam has a Max dex limit of +2 so actually reduces your +3 to +2)