Sketch plane axis orientation

I am currently working on this part. The idea that I'm trying to make work is for the end of the gray part to be parallel to the face of the blue part as the angle of the blue part changes. I made a plane parallel to the blue part's face and drew the sketch on it. It looked good until the angle rotated past 135 degrees. After that, the sketch dimensions rotate; it looks like that axis switch of the sketch as the plane rotates. I've spent quite some time working on this. Any potential solutions?