Okay look at it this way. most light saber hilts are straight except for some. but in the curved hilts the components are still straight.
in the ringed light saber all the components are on the same angle so when the blade comes out instead of being straight its curved.
so to make the ringed effect the blade is curved on a 360 degree angle.
now you probably thinking"but if its a 360 degree angle wouldn't it go through the hilt and bla bla bla. well the blade has been shortened so it only reaches the end of the hilt.
(is a bit unbelievable but who said anything about be believable, its not like their really are light sabers)