It's PPS
PPS: Each share receives a fixed reward known in advance. This is the ultimate low- variance, low-maturity simple method, but has the highest risk for the operator, and hence lower expected returns than other methods and risk of collapse if not managed properly. It is currently only moderately attractive, but is the way of the future - it will be the most widely used method when the infrastructure to offer it with low fees is established.
How much is the fixed reward ? I mean how is it calculated in terms of network difficulty and miner's hashpower ?
well they have a number for every th you mine with.
right now 1 th should earn 0.01237 btc a day I believe their fee is 4% so .96 x 0.01237 = what they pay for every th you give them
I think that comes to 0.0118752 a th not sure if that is the rate but it should be very close.
what is nice is they pay that daily. no worries about luck.
and here is the rate page
https://www.f2pool.com/help they say 0.01187958 for each th you send at them
I just sent 1 of my sp20's at them to see if I like them.
I see, but they alot more difficulty then other pools, but still are getting the most blocks according to blockchain