Thanks for the extensive design work on this one!
I was disappointed with the Mk3 overhang performance too, but the main issue I have is curling on the front side of objects with overhangs. I figured that the Mk3 shroud allowed too much air out the front and there wasn't enough back pressure to get enough of the air around the sides. So before I tried your design I did a little experiment that I thought might be helpful to you too. I just used my 3D pen to block about 50% of the front side and although it's not perfect I got a vast improvement in my overhangs... I'll post an image here:-