The way that the human eye judges size and proportion is actually quite complex. It is not as simple as a ratio of penis length to height. For example, if a person has a petite build, a very thin penis may look normal. But a thin penis will look longer than it really is. If on top of this, the person is short, he will appear to have an exceptionally long penis.
A couple of months ago, I was at a party (well, OK, orgy), when a rather hansome young naked man, playing with his hard dick, steps into the room. I was rather busy at the time, so I didn't pay too much attention, but he gave the appearance of being quite well hung in the quick glance that I did give him. He was probably about 5'-8" tall, with a slim build. The whole room sort of murmured about his cock as he entered, and when he walked out a few minutes later, I overheard comments like "nine and a half" and "ten inches."
Later on, in a different room, we both made for the couch at the same time, and ended up sitting next to each other. I wouldn't have thought I was his type, but he seemed to like sitting next to me, and started putting on a little show, stroking his big hard dick, while drinking a beer from a 16 oz "tallboy" can. So, I get myself nice and hard, too. He then shows off some more, by casually holding the tall 16 oz can in such a way as to compare the length of his penis with the can height. The tip of his penis extended just a bit beyond the top of the can. Then I sort of smiled, and knew it was all an illusion. Then he reached over and started playing with me. His little hands couldn't close around my girth. So, then I took his meat in my hand, and realized he was very thin, although it certainly didn't look that way.
Later at home, I measured such a 16 oz can, and found it barely 6.25 inches tall. So, his dick was no where near the the 9.5" inches that a couple of people mumbled, but more like a rather ordinary 6.5. The same people that judged him huge also probably felt he was bigger then me, when in fact the reverse was true. But our heights were not that different- just 4 inches out of 6 feet. The difference was that my cock is quite thick, which makes it look shorter, and his was quite thin, which makes it look longer. But, up against his delicate build, it didn't look like a pencil-dick, and instead looked quite large.