How much does Town Hall Level 9+ reduce the loot from opponents?

I was able to find out there is a loot multiplier for when you attack someone in matchmaking. The loot gained is affected by the Town Hall difference between the attacker and the defender.

Players get increased loot for attacking Town Halls of a higher level, and reduced loot for attacking Town Halls of a lower level.

Example: If an attacker has a Town Hall level 9 and a defender has a Town Hall level 8, only 90% if his total available resources is considered lootable.

Note: Matchmaking isn't set up by Town Hall levels, it is based on total trophies the opponent has.

Source

That's 90% of the 20% that everyone has available. Its always 20% available, then the multiplier comes into effect.