26 out of 30 is still an 87% success rate, no way a 5'8" guy has even close to that success rate.
It depends on if you're talking hookups, or dating. If a guy who's 5'8" is trying to pick up random women at a bar or something, then I can imagine him getting rejected more often on height alone. I don't think most men have a success rate of 87% in that scenario though, regardless of height or dick size. In terms of dating however, I think most guys won't ask a woman out until they receive some sort of clue that she's somewhat interested (I may be wrong, but that's how most of my friends go about it). In that case, I don't think being 5'8" would narrow the pool of women who would be interested in you that dramatically, especially if you're good looking and have other qualities they might find attractive. It's different for online dating I guess, where you can list your height on your profile, but then again men often lie about their height on those.
Even if it is 60% success rate that's still 40% failure. No way guys with avg dicks are facing nearly the same rejection rate. If you really think 90%+ of women are accepting of guys that are 5'8" you are living in a fantasy land.
What percentage of women do you think are okay with 5'8"? I'd say around 70%, although you might think different.
Anyways, when it comes to dicks it depends on the situation, and what you would consider a success or a failure. In a hook up scene type scenario, where people are only looking for sex, having a 5" dick with low average girth will be on the small side, as guys who gravitate towards that tend to be confident in what they've got (high average to above average). They might not get flat out rejected at the sight of their dick, but they may encounter a lot of one-and-done type situations where the woman is disappointed and never calls back. You could see that as a success, in that the guy got laid, but you could also see it as a failure as the woman is no longer interested in a repeat hookup, or was dissatisfied. In that situation I could see a guy with a 5" dick and low average girth having a "failure" rate of 20 - 30%, depending on what you see as a "failure".
Of course that changes when it comes to people who are looking for relationships.
I don't know how you can reach this conclusion. Have your friends ever been rejected? If so, how do you know it was not because of their height?
They don't get rejected often, actually. Mostly because they don't make a move until they know the woman's interested, and they mostly go for relationships as opposed to hookups. I remember when one of them got rejected in highschool, but the girl who rejected him started dating a short guy, so I know height had nothing to do with it. Also, they're both attractive, so they tend to attract women who are okay with their height. You could count all the women who wouldn't be interested in them in the first place due to their height as little "micro-rejections", but that wouldn't be fair since they wouldn't pursue women who weren't showing signs of interest, so it's not really a rejection.
One has a hard time actually keeping women though, but I don't think height has anything to do with that.
I don't have any friend's in the US who are under 5'7", so I don't know what their situation is like (I can only go by shit that's written online). All I can say is that two of my friend's who are around 5'8" are quite successful.