|The secret to keeping pleats set is to not move your fabric til it's dry and cool.
When you use a curling iron and them immediately comb through the hair it loses the shape of curling iron. If you leave curl "curled" until dry and then comb it it more difficult to get the shape right. The same holds true for pressing. Lets face it, Human hair is closer to Sheep hair (wool) than it is to polyester.
If you want a center crease to stay it pays to press and cool, press and cool. If you want pleats to stay Press and cool, press and cool.
I also use a wooden block to "pound" creases if I want them super flat....again, pound when hot and steamy, then let cool. You can also leave the wooden pounding black resting on the area til it cools. The wooden block holds in steam and heat so that the garment cools slower and allows for a better crease.