Sorry, but I'm not understanding your scoring system. I think you've been
inconsistent, which is why you're not getting the answers you expect.
If you want the Rank 1 to score 100%, and the separation to be 100% divided
by the "Out of" figure, then wouldn't 2 out of 4 be 75%, and 3 out of 4 be
50% (not the 25% you quoted), then 4 out of 4 would be 25%.
Of course if you want the 4 out of 4 to score 0, then you'd need the
separation to be 1 divided by ("Out of" -1), or 33.3% in your case, not 25%,
and that would give 100%, 66.7%, 33.3%, and 0% for your four scores.
Tell us which system you are using, and then you or we can work out a simple
formula.