Contact should be somewhere around where the lead arm can no longer hold its 90 degree angle correct? Here is how I introduce stop swings using pvc. We use whiffles on a tee next.To the point of contact. Stop swings to a point helps you focus on the hands and connection to the body. The arms are used less, accept for their role to the hands.
Try different levels of swings, 60% effort on a stop swing etc. You’re not interested in effort through contact.
Do 10 stop swings then a stop swing that doesn’t stop, follow through.