Trail Edge smudging on c6500

[dagoof]

Got a tricky one, getting a smudge towards the tail edge of the sheet on images or text with heavier toner coverage.
Lighter coverage graphics in the same location are fine. It's quite a rigid stock, I thought it might be stalling in the fuser but tried the same stock on another machine and it was the same. So I think it might be flicking the tail edge after coming off the separator.

Tried adjusting back AC/DC separation values. Any other tricks, maybe reducing toner density?
Attached a scan of the problem, image is about 30mm wide, you can see the smudging on the 2 "e's" (and areas above) which are exactly 25mm apart.