The math is tricky! I had to go through a dozen permutations by hand before I finally found the correct one. But generally yes, you have two things to deal with: The probability of the inherited IVs lining up correctly, and the probability of the inherited IVs NOT lining up correctly. And of course within that you have to worry about whether the correct parents IVs are passed down AND whether the randomly generated IV works out how you want. If both parents have the same IVs, it works in your favor as long as the correct IV spread is inherited. Needless to say, its a pain in the ass and not easy to wrap one's head around.