User blog comment:Admiral Leviathan/Corporate Espionage (OHAtW 64)/@comment-5215338-20130524141109/@comment-11644326-20130524204934

It's all about proportion. While Sonic may seem much taller, his head is far oversized and out of proportion when compared to the soldiers (Which, I clarify, ARE humans).

If Sonic had a normal, Human-sized head, he would be only slightly taller than the soldiers.

Of course, I'm still sticking to Sonic's Canon height (Roughly 1 M), which means that the Humans are all about the same size anyway. Let's just assume that stuff changes in the future and Humans smallify or something.