Franco has it mostly right.... Forming the foot box will take up 6-8 inches of length.... Also, the forming of the shoulder pockets and having suficient length to reach the ground beyound the shoulders is a factor (Hammockers up to 6 foot can get by with a regular length.... because the hammock rises beyound the shoulders to meet the top quilt where the ground does not...)
Also some folk at 5-11 to 6-0 feel they can use a regular.... However, their sleep style may be more open and or they may actually pull up on the footend and actually compress the foot box loft in doing so.... The practical limit of the No Sniveller for ground dwellers is 5-10.
PS If you have not noticed JRB's Trail Days sale is again open to all, via the web, and the No Sniveller is $ 40 off....regular and long.