I purchased a yurt without insulation for which I've made some. I'll assume you aren't a geometer, so saying you should make an annular section to match the truncated cone that is your yurt roof is probably meaningless (though gives you good search terms).
Simply Differently, a website by a fellow that has made & lived in things like yurts, tipis, & geodesic domes, has an excellent breakdown of the math and a calculator to show you different ways to match the geometry.
I believe the reflectix is normally taped together. Duct tape kind of works, but I think the manufacturers also have a special tape. Or aluminium/ducting tape would likely work.