Fix Deep Creases Under the Backside
This is a pattern correction for people with flat backsides or forward-tilted pelvises. You can get a lot of excess fabric in the back here.
To see if you can correct this area effectively, pin the excess up and then try moving around a little. It might be a little bit of a fisheye shape. If you can move around ok with it pinned, it means you can eliminate that excess.
Draw a line where the fisheye was (across the pattern).
Draw a line from the front rise to the center of the fisheye.
This is a slash-and-close correction. Cut along those lines, pivot, and tilt to close as shown.
This information and more can be found in The Fitting Book. Order your book today through the link below.