Cutting Angles (Zircon)

Now I’m just confused. I’ve always been told & read to make your Pavilion angles 1.5-3 degrees above CA, so the light will not just exit & cause windowing. Not as clear on the Crown angles, but I’ve always assumed that it should be slightly below the CA, so as to let the light go thru to the Pavilion angles, except on the outside, where they should be higher to more or less "Capture the light in the stone.
Have a piece of Zircon. 1st of all I’ve seen 2 different CA’s (30.4 & 34) (Which do I have ??). Also, been reading where people have said NOT to do 33 or 36 degree pav cuts because it causes “Tilt Windowing”? and to do 39-40 degrees?? Then on the Crown, I would normally do 28-32 degrees to make sure the light gets thru.? HELP! Can someone help me out here? & elaborate on the Why’s. What angles should I be using for this Zircon?
Is there a list that shows preferred angles to use?