While the way you worded that doesn't convey the rule exactly, I think what you meant to suggest is correct, so I think we'll accept this as a victory.
For reference, I had two ways in mind of wording it:
a. "AKHTBN if the number of letters before the first vowel is the same as the number of letters between the first and second vowel"
b. "AKHTBN if, in the first (N * 2) letters, the Nth and (N * 2)th letters, and no others, are vowels"
Not that it ever came up, but I was not considering "Y" a vowel for this one.