I did experiment with ways to draft these by pure mathematics but once I realized the decreasing width of the flounce created ellipses and the difficulty with calculating the circumference of an ellipse, especially concentric ones with varying radii, the graph paper method was much, much easier. This one starts wide and ends narrow, the amount of flare diminishes towards the end. But like I anticipated, theres more to drafting a circular flounce pattern. I believe you created a logarithmic spiral, (true??) Two times also works ok.