I'm having the same problem, but mine is a tiny little thing. I really like yours and wish I had that much space.
Years ago I helped a friend of mine install a shade almost exactly like you have there and it worked pretty good. I didnâ€™t do that on mine because of the direction my planter box is and I wanted easy access to everything, but if not for that Iâ€™d do it exactly like you have. I have a shed that helps in the late day, but its full sun in the morning until about 3PM