KK's vaginal barrel is about average depth - 5" - 6", depending on how aroused she is. I'm long enough to penetrate her fully, and engage with her anterior, and posterior fornices. The more aroused she is, the more comfortable that deep penetration is.
KK is a size queen, and needs at least 6" of hard cock to reach those spots. 9" is her "sweet spot." She prefers female-superior positions, so that she can control the depth, and pressure of penetration. KK finds it unpleasant, and a sign of a poorly skilled lover for some guy to just start plunging away with abandon, not understanding the banging her cervix can be painful.