I am fairly new to Illustrator and wondering if it is possible to achieve what is on the screenshot attached. I added 2" of down spread to a rectangle & maintained both the height throughout at 3" and the top length of the original shape (5").
In this case I don't think that it is easy to use a Warp effect if it is crucial that the upper segment of the rectangle should remain the same length after bending it.
To get nearly precise results I'd recommend to construct it with the help of a pattern brush, followed by expanding its appearance.
You can obtain this (kind of) change of shape by using Effect>Warp>Arc with a negative Bend, but Arc is symmetricel so you have to group the rectangle with an identical one that get the mirrored bend, and the calculation is quite different.
The program in the screenshot is Richpeace Garment CAD.
The curve isn't as important just as long as the upper length of the rectangle remains the same (5in) and there is a 2in spread at the bottom. All while maintaining the original height of 3in throughout the shape.
I've used the curvature tool after making a new rectangle with my desired measurements, however I don't achieve the 3in height...some spots will be 2.91in. or 2.97in.