Not sure if your idea is correct.
A lot of people myself included struggle with this:
[....]
Two ways to calculate your expected earnings per second
1. (best method) yourhashrate / 2^32 / difficulty * bitcoinreward
2. yourhashrate / networkhashrate * network blocks per second * bitcoinreward
You were forgetting how blocks per second changes when the network hashrate increases and difficulty stays the same. And don't forget the part variance plays.