What in the world? Well you can see that flap on left has plenty of JB on lead edge. Sanding on radius is far more time consuming than sanding flat areas. Since you are point loading at contact area you need to be very careful about sanding away your fiberglass. On flat areas you can put exorbanate amount of pressure and sanding goes nicely. On radius you need not very much pressure and a coordinated bias articulated stroke using eyechrometer/feel/straight edge to locate locate high spots and remove.
Y8-10-15