Well I played a bit more with the location of the point and the size of the pocket envelope and I got something closer to what I wanted
Not sure how it works... it seems that the starting point needs to be inside the "hole" meaning you have to offset it to the inside by the tool radius.
On the last line of each pass the tool comes back by retracing where it just milled. I could not figure out how to avoid that... I suppose we could reduce the step... but it would be better if the tool started on the left instead of starting on the right, because that edge is more critical.
BTW, the tricks Allen showed us with HSP work here too, but I wanted to also learn to better use the standard pocket feature because it is so much simpler for some geometries