The average vagina is also 4" long fully aroused, and contrary to what a lot of AVN LIs proclaim, having your cervix rammed during sex is not pleasant for most women. Not to mention that extremely girthy penises are more likely to result in painful vaginal tears and urinary tract infections.
Since we're citing studies though, there have been some that investigated size preferences empirically.
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one for example found that women prefer, on average, an erect penis size of around 6.4 inches in length and five inches in circumference for one-time partners and preferred a slightly smaller penis of about 6.3 inches in length and 4.8 inches in circumference in a long-term relationship, compared with what they wanted in a short-term relationship. There's a reason that the average sex toy falls into that range.
This does make it bigger than the average penis size of 5.2 inches long and 4.6 inches around. But multiple studies have shown circumference is far more important than length when it comes to preference and sexual satisfaction, and female orgasm success rate drops of dramatically with penises longer than 8-9", according to surveys.
Point is, if you want an MC with a penis that
actually will be preferred and enjoyable with lots of LIs, a slightly above average one is more realistic than a 10" monster with a wrist-like girth.
But these are AVNs and sometimes porn logic prevails.
