Samifer's bustle was made the same way as mine, using this tutorial. I originally was going to make a trained bustle, since her dress will have a train, but upon further research a number of people who have made trained bustles have been disappointed by the results. Add to it a few images of beautiful trained gowns wore by ladies stating to be wearing a lobster bustle underneath, and I decided to go the easy path. The bustle is longer than mine, and should hit around mid-calf. It also has a box-pleated ruffle along the bottom to give it more poof.
Right now I'm playing with the proportions of the bustle. For mine, the smallest bone (closest to the waist) was 2/3 of my waistband measurement. (The waistband is 2 inches below natural waist, which for me is 30". So my smallest bone is 20" long.) I felt it was a good size, but I didn't know whether that system worked for everyone. So this is my test. I used the same proportion for Samifer, and I'll see how it looks. If it works for Samifer, I can extrapolate that it will work for Gabriel since she is a similar size. The true test will come from Crowley and Castiel, who are the farthest points away from the mean in either direction.
And now you know two important things about me. One: I play Dungeons and Dragons (technically, I play Pathfinder, but I call it D&D since more people are familiar with that), and Two: I have taken statistics.