Pleating on a sewn shirt

Hello, Blender community!

I’m a newbie when it comes to 3D and Blender, and would greatly appreciate your help! I wanted to make a kind of a long, simple-cut folk shirt with shoulder insets and pleating around the neck (0). My objective is to use the model for my painting studies, where I will try to analyze how the folds look like with different light set-ups, so the model should be quite detailed, but does not need to be optimized for complex scenes. That’s why I’m not really interested in achieving the pleating effect with texturing, but would rather like to simulate it with cloth physics and get the most realistic result possible.

Following some tutorials on cloth sewing and making cloth folds, I have created a set of planes that are connected with bridge edge loops (1) and added shape keys to the neckhole-edges grabbing every other vertex and scaling with proportional editing (2). I have also inserted the shape keys into the keyframe. Still, the cloth simulation seems to be unaffected by the shape keys (3a, b), as if the shape keys were “to weak” to keep the cloth gathered like I want it to be. What am I doing wrong?