The 6.4 is atually in the y-direction (vertical)
1 16 0 4 0 0 0 -8 0 -6.4 0 -8 0 0 t04o6250.dat
Horizontal in x and z direction the outer radius is 13 (8 + 5)
That comes from 8 being the major radius with the minor being 0,6250 of the major, that works out to 8 x 0,6250 = 5
The slight gap is due to the scaling up of prims as Philo noted
Edit: The 6.4 work out to a scaled height of 4 LDU
1 16 0 4 0 0 0 -8 0 -6.4 0 -8 0 0 t04o6250.dat
Horizontal in x and z direction the outer radius is 13 (8 + 5)
That comes from 8 being the major radius with the minor being 0,6250 of the major, that works out to 8 x 0,6250 = 5
The slight gap is due to the scaling up of prims as Philo noted
Edit: The 6.4 work out to a scaled height of 4 LDU