To your question you sent me on FB
Not like the lawn mower drill, that can get the elbow behind the shirt seam. More like the upper right arm folds softly just in front of your lat. Basically if someone was to put their hand on the side/front of your rib cage at address, you would want to lightly squeeze their hand from A1-2. When the arm stays straight,you won't be able to "squeeze" that hand and that's when the club gets in and the upper arm slides behind you.
Green line represents the shirt seam, blue dot is the middle of your upper right arm. The upper arm is gently folding into the side but in front of the shirt seam. Then you keep stretching and bending. The upper arm will come off the side a bit, not trying to keep it "glued" to you, but the arm/elbow won't go "behind" you.