That vertical picture of the "primer bird" also shows a very strong fence at the base of the canards, that fence extends aft onto and over the inboard leading edge of the main wing, and there are no doubt several reasons that is carried aft onto the upper surface of the wing.
Also note the very active "vortices", many of you may recall that I used to lament endlessly about wanting to see the J-20 in the wind tunnel with "blue smoke". This isn't blue, but it is "visible airflow", and while I would love to see a full profile of the J-20 through a full normal flight profile, take-off, climb, cruise, transonic-supersonic, high-alpha and post stall, through landing, this is at least a "teaser".
As the J-20 likely transitions from a fast pass airspeed of 400+ knots, and pulls to the vertical, he's prolly at least 250+ knots, pulling enough G to energize airflow and produce "vapor clouds", that vertical primer bird, shows the very tight tolerances of the serrated edge plates that make up the upper fuselage.