another newbie question

to calculate so called "luck factor" to estimate progress in finding solo block, is it a matter of dividing current number of shares with network diff?
e.g. at the moment of writing for the whole pool 4819841797984 / 26690525287405 = 18% ?
kind of
but to understand this a bit more.
a die is 1 to 6
6 is the winning number
rolls of six should hit at an av erage six rolls
but can hit in a roll 1/6 = 16%
or in 12 rolls 12/6 = 200%