?? Not sure we're referring to the same issue here. In question was the 20 mm wide stitching across the spine pocket 10 mm down from the nose. The presence or absence of that seam will not appreciably change the position of the leading edge spars in the nose pockets nor the overall shape of the nose. That seam does allow a narrow nose to fold up a little easier when packing up the kite.
Of course how far the spine slides into the nose webbing will be affected. Compensations may be needed to insure the spine length and center T position are as intended.
Moving the upper spreader connectors relative to the overall sail would
change the effective length of the upper spreader and would affect the nose shape.
The nose 'cup' does seems to effect the fade. It gets more stable and harder to get out off. With my Sixth Sense's i've lowered the topspreader for the same reason you've altered the lil' monster's nose.