CARLWORKS

The 6% is the Estimated ROA (Return of ADA, annualised) based on staking result from last 30 days. The calculation is also based on delegator rewards. The 3% margin is for the stakepool operator's share of the reward. This could be change anytime by the stakepool operator. The rewards per epoch are distributed to the delegators, meaning the more delegators a stakepool have the more will share the reward pie but if you stake in a smaller stakepool you may not always get the reward per epoch but once it gets a reward your share will be larger. Also by staking to a smaller stakepool you could help it to continue its operation or do its purpose and at the same time help cardano to become de-centralized.