My pool can confuse people just ask Rich but this is how I think it works for Lexicon/uray pools.
Each round your best dl receives shares and if the current block isnt won it goes to historical shares (All rounds)
Let say the pool wins a block!
60% of the block is paid on the Current round. 1937 (Block reward) * .60 = 1162 burst.
So 1162 burst will be paid to the Current round. Each round has a total share let say its 8000 this winning round.
You have 1000 shares what are they worth. 1162 / 8000 = 0,14525 burst so 1000 shares = 1000 * 0,14525 =145,25 burst.
The same is done with historical share(all rounds) but there are other small factors they could change the payout. It will add your current and historical together during payout. You might receive less cause you just started.
If you got a lot of shares then it must be good! It dont matter if its % or shares the number is not fixed it changes every round!