Usually when I’m trying to find the scapula I follow the acromion process and then I try to find the infraspinatus, or rather the dent it creates next to the trapezius. I think you did a good job at finding it in these studies! Though sometimes it looks like it’s too close to the rib cage (especially in the last drawing, I think it may be because they’re pointing inward too much). The main mistake I found is that the teres major is too large, which is making the infraspinatus look too small. Proportions do change from person to person, but it seems more like you haven’t completely understood its function or form (I’m mostly referring the the first drawing). Since it’s main functions are to help bring the arm down towards the body and extend it to bring the elbow back, it is extended when the arms are raised. The infraspinatus laterally rotates the arm, so it’s usually flexed when the arms are raised. In the first image, the teres major is being stretched, so it should have a shape similar to the right one in your last drawing. If you check out the eBook, the teres major has a shape more like a cylinder whereas the infraspinatus is more flat and wide. I think because the shoulder muscles don’t all flex at the same time, it’s important to understand their individual functions and shapes. The eBook is very helpful, I strongly recommend you take a look. Hope this will be of some help!