I have a question regarding the allowable height of a PVC toilet flange above a tile floor. The Oatey screw and set PVC flange insert into my 3" cast iron waste line sits on top of my new tile floor. The thickness of the flange top is 1/2" . So the flange height is 1/2" above the floor level. The flange top is screwed to the floor. I have purchased a new Kohler toilet. A dry set of the toilet on the flange gives a little front to back rocking motion. I have purchased a wax free horn/flange guide. When I have set the toilet and tightened the flange bolts, the result is even more severe rocking from front to back on the toilet flange.

1. Is the flange level too high?
2. How high above the floor level is tolerable?
3. Are there screw and set flanges with thinner than 1/2" rings?
4. Should the flange be flush with the tile floor?

Please help.