O.P. here... MY simplistic 'brain', at the
current moment anyway...), tried to solve this by Reverse thinking!!!
Or at least from a totally different '
Angle'... (excuse the pun, but
NOT actually a 'pun')

Consider a perfect circle. Ok, the calculation of it's 'circumference' is OBVIOUSLY
C = 2 Pi r.Now rotate that circle 90-deg until it '
appears' as a straight line!! Now the APPARENT (from the viewers perspective!), is just
2 x D 
So to ME!, all the 'InBetween' apparent 'Circumferences,
from one's view point!, while observing such an apparent Circumference, MUST
simply be not only between those 2 above limits, but MUST be directly related mathematically as a result of that
specific angle we are viewing
it from? 'One' needs to let go of thoughts about a 'physical' Ellipse per-se, and one that is '
apparent' from the angle we are viewing it!?
Surely then, the actual 'Maths' is simple!! Without those complex theorems/styles being applied?, or 'trying' to apply them ??
