Got a few tricks I use I'd be glad to share.
1. I use the petal method on my own designs, but there's a little cheat that helps with the shape. At the base of the cut on each side of the petal, I add a horizontal slice across the point where the petals meet. it looks like this:
The orange lines represent the cuts. Sorry, crappy drawing. My models look much better than this.
Another trick I use is to apply thin CA glue to the rounded part and sand smooth when dry. I did that with my North Korean HS-16, but the structure uses both stepped cones and petals:
Once the CA soaks into the paper fiber and dries, it becomes hard like plastic, so it can be sanded. Then, I painted the nosecone. This also works to strengthen load bearing structures like the engine truss at the bottom of a Titan or the lattice work between stages on a Soyuz or Long March.