I had to reinstall the compression plug in my carbon fork and wanted to know how far below the top of the steerer to put it. Is it the same as a star nut, 15mm?

Also, previously when i was tightening the top cap of the headset it didn't appear to cinch down all the way and the screw kept on turning. Am I doing something wrong? The headset seemed like it would never get the bearings to bind no matter how much I would screw the cap down

Any help would be appreciated. Thanks.

most plugs take 2 different sized allens.
smaller one for the expander part and a larger one for the top cap.

My Reynolds plug did not have enough friction to allow the expander to "bite" the ID of the steerer. I roughened it up a little with some fine grit sand paper. Problem solved.