If you place a straight edge on the top of the WD-716 frame assembly between the forward channel and aft round tube you see what I saw.
The skin is not going to lay flat on the forward upper channel flange?
I used my belt sander as seen in image 2 and 3. The aft round tube is elevated flush with the height of the belt. Then, just slide the frame side to side to remove material from the aft edge of the upper flange, just like the plans say to do.
As a result of removing a bit of material from the Wd-716 upper flange, aft edge, we now have a flange that's in the same plane as the aft round tube. The Canopy skin will now fit nice and flush on the flange.
Canopy fitting, RV-7A Tipup
Rebuild project, RV-6A Slider