Thank you for your replies guys, you have been very helpful.

In case someone else may be interested you can see my updated formula below:

bitcoinPerDay = ((minerHashrate * (blockReward + avgRewardFee) * numberOfSecondsPerDay) / (estimatedNextDifficulty * 2^32)) * poolFeeMultiplier;

For reference:

I have used the API from BTC.com to calculate the average block fee reward of the last 8 mined blocks.

• Documentation: https://btc.com/api-doc#Block
• Endpoint that I have used to get all blocks of a given date: https://chain.api.btc.com/v3/block/date/20200730

The results of my FPPS calculation are now also pretty close to the results of the mining calculator at https://btc.com/tools/mini-mining-calculator.
The accuracy may be improved by including more than 8 blocks into the average block reward fee calculation. I will be testing this, but for now I am quite happy with the performance.