OK. I think I have solidified a small but important point in my brain. Here’s the legal set up for the set position:
For the set position, the pitcher shall have the ball in either his gloved hand or his pitching hand. His pitching hand shall be down at his side or behind his back. Before starting his delivery, he shall stand with his entire non-pivot foot in front of a line extending through the front edge of the pitcher’s plate and with his entire pivot foot in contact with or directly in front of and parallel the pitcher’s plate
So now I think I have locked in that the PIVOT foot has to be in contact with or directly in front of AND parallel the rubber, while the front foot just has to be in front of the rubber and CAN be open to 1st.