OK a couple of things…
It looks like that pool is on PPLNS… That’s Pay Per Last N Shares.
So, when you start mining, you will not earn at your full hash contribution rate; you need to mine for some time before it ramps up to full earnings. (I’m not sure exactly how long.)
After that ramp-up is complete, you’ll earn at full rate, 100%.
When you stop mining, you’ll continue to earn, even though you’re not mining. This “ramp down” compensates for the “ramp up,” earlier. It balances out - you’ve earn based on your full contribution after the ramp-down from 100%.
Why do PPLNS pools do this? Because it discourages pool-hoppers. The pool-hoppers try game the system, jumping between pools based on when they find a block. Coming in and out is bad for the pool - and it takes money away from the steady miners. The ramp up / ramp down process doesn’t penalize anyone who mines long enough to reach 100% earnings, but it does penalize anyone who jumps in for just a few hours and leaves.
If you only ramp up to 50% and then leave, you’ve ramped up from 0% to 50% and then back down to 0%… on average, you’d only earn 25% of the hashpower you contributed while mining, and then another 25% after you stop mining, for a total of only 50% of what you contributed. You have to stick around long enough to hit 100% to get your full earnings.
Yes, 5k looks a reasonably expected rate for that combination of GPUs’ hashpower, based on WhatToMine estimates. The actual reward rate you’d expect will fluctuate because hashpower moves between coins, and coins change Difficulties to compensate, and earnings will depend on the actual Difficulty… but your earnings should be closer to 0.2 BTG than to 0.04 BTG, assuming you stay long enough to reach full earnings rate.
But that’s an expected average. Which brings up…
Your earnings also depend on the pool’s luck finding blocks during the times you’re earning shares. In a given period, a pool may find more blocks than expected or fewer than expected, and that will dictate your earnings.
Looking at that pool’s blocks mined for the past few days, they have been finding blocks much slower than expected, on average:
On 2/7/2018, the pool found a block much quicker than average - two times - taking 32% and 16% of the expected effort to hit a block. But, during the most recent blocks - during the time you mined - they have had worse luck than expected.
These effort numbers are estimates, but if everything is working right, I believe these numbers should average out to roughly 100% over time (if I’m not mistaken). This may be a run of bad luck, unless there’s some sort of problem at the pool.