Why wasn't Perry decapitated??

I'm reading about hangings atm, and I found this:

Decapitation long drop: For almost anyone, a directly vertical drop of more than 7 feet between the ligature point (where the rope is tied) and where the noose meets your neck will cause decapitation (providing the noose doesn’t snap). This is obviously variable depending on your weight but as a rule of thumb even the lightest people will be decapitated at 7ft.

Perry had more than 7ft between the ligature point and where his neck eventually landed beneath the platform, so why didn't his head pop off? Did they exaggerate the length of his fall for the movie or did inmates really fall that far beneath the platform? Wouldn't it have been sufficient for the floor to simply fall away and the inmate not fall any distance at all? That's what I figured was going to happen, since the rope tied to Perry appeared to have no slack at all. Yet somehow when the trap door opened, he dropped his own height + another 3-4 feet. So he fell at the very least 8ft assuming his noose was tied around his neck at approximately 5ft above the platform and he fell at least another 3ft below the platform.

What am I missing here?