A friend recently made her first self-patterned corset, and was asking me about how to avoid those pesky little wrinkles the happen at the hip and bust. In my experience, they are usually caused by one of two things (or sometimes both).
It can be caused by improperly placed grain of the fabric. Due to the outward spring of the hip (or the bust), it alters the line of greatest pressure such that it’s not perfectly horizontal. Instead, the pressure on the panel angles towards the apex of the curve. If the bias of the fabric falls exactly along this stress line, it creates wrinkles, like pulling on the bias of a square of fabric. There will always be some bias stretch along this area, but if you have a lot of hip spring, it can be worthwhile to tilt the grain of the fabric slightly so it’s not full bias at the front of the hip or the side of the bust (thankfully, with most vertical panel patterns, tilting one also tilts the other very nicely). Another way to solve the problem is to use a hip gore, which I’m pretty sure is why on extant Victorian pieces it is so common to see gores used for corsets with a dramatic hip spring. This problem is also minimized if the next cause is taken into consideration.
Wrinkles along curves can also be caused by too little pressure underneath. That is, the stuff that is the wearer is not sufficient to hold out the form of the corset, so it collapses slightly and tugs in ways it’s not meant to do. If there is a lot of pressure underneath, you won’t see any wrinkles even if the line of greatest pressure is along the bias. So, soften the curve slightly, reducing space where you see wrinkles. Alternately, you can pad it out with some soft foam.
Keeping those two things in mind can help, whether you are drafting your own pattern, or modifying an existing pattern in search of that perfect fit.