I can see that there are many ways the algorithms for fair work-sharing could be constructed.
There is 1 and its simple. How many shares were submitted this round in total and what percentage was yours = your % share of the block.
The rounds get skewed with PPLNS but it's the same thing. what percentage is yours.
If you look on the dash board on the right hand side it will show...
Pool Valid 671,670
Your Valid 16,072 (these are mine)
from that you can work your percentage of the block.
as for the luck factor/block find times - there's just no way of predicting. Speaking of luck, had you have stuck with us or started our 24 hours 1.30 ago, you'd of already bagged 0.7 MAX.
