I named this technique Shoulder Sink in and Press away 🙂 Back to practicing on my husband. I've tried to do something like this before but didn't have your detailed instruction and so my hand placement and the second part of pushing shoulders away as the hips sit back didn't happen. With your instructions the two movements link effortlessly and I felt confident with my hand placement. The one thing I needed to keep in mind was the slant of his chest and making sure that I was using a 90* angle. My husband loved it and the technique was easy and rhythemic and beautiful!
I found the work on the sternum a little more tricky. I've worked in a lunge position facing the chest before and worked my fingers from the sternum out between the ribs. This was easier for me to feel where my fingers go. But sitting behind my husbands head, and thumbing down between the ribs ON the sternum was harder for me. First, my husband said my thumbs were too pointy, so I flattened them a bit and that felt better. But it was hard to feel where the sternum ended and the ribs began and I could see my thumbs getting wider and wider in order to find the dip between the ribs. This seemed to be superfluous to him because he said it all felt good. He also enjoyed the loose fist pounding and Thymus tapping.
The sternum work IS a bit more 'tricky'. However the thumb work can also be replaced with simple palm circles on the sternum or edge-of-hand circles on women where the palm doesn't fit easily between the breasts. So you can do the more intricate thumb techniques or the the easy circling techniques - both will feel good.