I second this, but at the same time the vertical tail of the J-20 on the right also seems to be higher (the tip higher than the back wall, while the left J-20's tail does not) it may mean that one of the 2 J-20 is parked more to the front relatively (thus potentially invalidating our analysis on the canopy height), but quite possibly it can also be that the twin seater have enlarged vertical stabs, which seems quite likely given a larger and possibly higher canopy.My somewhat less comprehensive but I think equally understandable comparison based off that original image lol
View attachment 78469
I've attached a crude handiwork of me trying to draw parallel lines on the picture, hopefully it will make my point a bit clearer =P