"Depends on the manufacturer"
second that....
also, the riding style, terrain, and bike geometry play a big role......If you are riding aggressively on rough terrain...you would want some clearance...
"I'm 5'8". 30" inseam and have 17", 19", 20". and 21" bikes...all fit very well.......The 17" MTB has a 15" BB height, 32" standover, and a 24" top tube..."
You have a 30" inseam and your bikes standover height is 32" and you are saying that it fits you well. Have you ever crashed while riding this bike? How did it go? unless you love to rough up your private parts, thats not a recommended fit. but hey, if it works for you and if you dont care about seriously injuring your boys....go crazy...