This mechanism guarantees that if User(A) has a block of 1,000,000 coins, and User(B) has a block of 100,000 coins, and both user's coins are the same age, both users have the same chance of staking a POS reward .

Both blocks will only gain a max staking weight of 100,000 coins per additional block. This is an anti-competitive staking measure. If you have a block of 100,000 coins, you have an equal, or fair chance to stake a POS reward.

Fair Weight determines your chances to stake, not the amount of coins rewarded.

Fair Weight 2 (FW2)  also known as your PIR (Personal interest rate) Is the mechanism that determines how much your reward will be.