It is VERY easy to calculate your expected reward on any PPS/FPPS pool if you simply look at your accepted shares on your miner.
I very much doubt any of the big pools would get away with claiming PPS or FPPS and not paying it, since it is so damn simple to check.

Running a rental from fuckhash is probably the worst way to test a pool, since you have no access to the miners at all, and no access to statistics, just a randomly allocated hash rate that may well be nothing like they say it is and nothing like you paid for.
We run a 'solo' fun run in my pool using fuckhash, and looking at the expected result vs the actual result, it's quite obvious they like rounding things down.

ALL pools work off share difficulty - hash rate is simply a calculation from that.
Alas when fuckhash only show you hash rate, it's really hard to tell what's actually going on and how much you lost vs what you should have got.

I do hope your pool also supplies valid statistics and isn't hiding behind unreliable calculations.

Aside: miners also do the same thing to show hash rate, it's also a calculations based on nonce difficulty found by the chips over time. (and it's also not a count of hashes)