The big characters should and will still have advantage
If you take any object - and make it bigger - the area goes up to (in simplification) - to power of two, but volume, and so as weight goes to 3rd power...
And that's why bigger is better, you have more strength (more muscle mass), you have height advantage, and you need to cover only little more area that average.
I don't have mind today to do math, I don't know if the 15% is to much or too less for smaller/bigger armours but is not that simple...
Still I like the idea that 200cm guy can't fit in 140cm person armour/clothes.