i think i may have found something to help you guys. i was looking at that old thread ridin' posted and then read what mick said about the grass building up on the back of the discharge and then dropping. i noticed on every deck in that old thread they have a piece there where as on the vx4 there isn't a piece. i circled it in this pic. perhaps you could try to weld a piece like that in the deck and see if it helps???
i saw where mick tried it. perhaps you could try to change the angle at which it's welded until you find a sweet spot???