Possibly by a percentage rather than a fixed number, so high dodge units suffer proportionally to low dodge units. Or even better, by a percentage but have a minimum dodge reduction number too for heavy armor.
Does Champion Armor have penalties, or not because it is special magic armor? I would be comfortable with no penalty, and everyone can wear, because it is late game gear and very expensive too.
Also, you will have to work out where Light Plate and Masterwork Chainmail sit in all of this. Maybe instead of Chain Mail Proficiency, you have Medium Armor Proficiency (includes Light Plate and Chainmail) and instead of Plate Mail Proficiency you have Heavy Armor Proficiency (includes Masterwork Chainmail and Plate) and there would need to be some sort of disadvantage for Light Plate and advantage for Masterwork Chainmail, otherwise they would always, and never, respectively be picked as Faction Traits in the new system.