One common complaint about 4e equipment is that plate armor (and sometimes other armor types) doesn't cost as much as it "should," given how much harder it is to make than other armor types. Here is a possible fix that leaves as much as possible about the AC progression unchanged:
1. There are only three types of armor: cloth armor (uses AC bonus, masterwork progression, and other stats equivalent to cloth), light armor (uses AC bonus, masterwork progression, and other stats equivalent to leather), and heavy armor (uses AC bonus, masterwork progression, and other stats equivalent to chain)
2. Hide armor proficiency is renamed "Light Armor Training" and gives +1 bonus to AC while wearing light armor. Scale armor proficiency is renamed "Heavy Armor Training" and gives +1 bonus to AC while wearing heavy armor. Plate armor proficiency is renamed "Improved Heavy Armor Training" and increases that bonus to +2.
3. Nonmagical light armor is described as leather, and nonmagical heavy armor is described as chain. "Magical" light armor can be described as hide, and "magical" heavy armor can be described as scale or plate (with the increased AC coming from the 'improved armor type' rather than actual 'magic')
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Effectively, the way the system currently works is that you choose an armor type within one of the categories (light or heavy) based on what you are proficient in, and the game makes the higher level armors not cost much more because they still want 1st level characters to be able to choose it.
What this house rule does is still allow players to get the AC increases their proficiency is designed to allow them, but move the different armor types into the magic item system, which is designed for a cost/power tradeoff.
1. There are only three types of armor: cloth armor (uses AC bonus, masterwork progression, and other stats equivalent to cloth), light armor (uses AC bonus, masterwork progression, and other stats equivalent to leather), and heavy armor (uses AC bonus, masterwork progression, and other stats equivalent to chain)
2. Hide armor proficiency is renamed "Light Armor Training" and gives +1 bonus to AC while wearing light armor. Scale armor proficiency is renamed "Heavy Armor Training" and gives +1 bonus to AC while wearing heavy armor. Plate armor proficiency is renamed "Improved Heavy Armor Training" and increases that bonus to +2.
3. Nonmagical light armor is described as leather, and nonmagical heavy armor is described as chain. "Magical" light armor can be described as hide, and "magical" heavy armor can be described as scale or plate (with the increased AC coming from the 'improved armor type' rather than actual 'magic')
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Effectively, the way the system currently works is that you choose an armor type within one of the categories (light or heavy) based on what you are proficient in, and the game makes the higher level armors not cost much more because they still want 1st level characters to be able to choose it.
What this house rule does is still allow players to get the AC increases their proficiency is designed to allow them, but move the different armor types into the magic item system, which is designed for a cost/power tradeoff.