Turns out that I was using the wrong length gas struts. Once Malcolm saw my pictures, he noticed that my strut was longer than he was used to seeing. So I picked up a 12″ (extended length) strut from McMaster-Carr, moved the hardpoint and voila! Door stays up when open and doesn’t distort when closed.

Here’s a picture looking forward from the back of the plane with the door closed.

Notice how the direction the strut is pushing is inboard of the hinge. Before the direction of force was outboard of the hinge.

Outside view.

Now I’ve just got to make the hardpoint permanent (it’s only temporary now), patch the holes in the B-pillar and repeat the whole install process on the pilot side door.