Why not do it Wurm's way ? It's more enjoyable for everyone, more realistic (there WERE very heavy xbowmen with 2h swords and plate armors !) : Each type of armor, depending on its weight, and type at all (how it is made), should give maluses to ranged weapons. For example, Cloths / naked : 20% bonus to accuracy and rate of fire when using bows, 5% when using crossbows
Novice Armors / medium leather : 5% bonus for bows, 5% for crossbows
All mediums except for leather : 10% malus for bows, 0% malus for crossbows
All heavies except for leather : 40% malus for bows, 10% malus for crossbows
Heavy leather : 25% malus for bows, 5% malus for crossbows
Royal Armors are same as heavies. Yes, maluses and bonuses are way less for crossbows, because shooting a crossbow doesn't require a lot of agility, so you can be effective with one in heavy armor : you just have to be able to reload it and aim it, and an armor does not prevent you from doing that.
So, how about this ?