This calculator is based on the article Examining Influence Requirements.
It determines the probability conditional on having drawn enough power in the first place. The reason for this is that it isn't useful to have take into account cases where you don't draw enough power when trying to determine how many of a particular faction to play. If you brick on your 5th power for 3 turns and can't cast your harsh rule on curve then was the problem the number of justice sources you were playing? No. When deciding how to build the manabase we don't care necessarily about total number of sources (i.e. likelihood to hit x power on turn x) we care about the division of influence so that we can cast our cards assuming we do draw enough power.
|# of Good Sources||Percentage|