[AusF20/F48]

The main difference (apart from the number of doors) is that the side sill on the F21 M sport is similar to the standard F20 sill ( the shadow line curves up not down)so the rear panel looks higher when viewed from that angle

Also, you have to consider
The front door is longer than the F20 so only one vertical line is shown in the rear half side view. There is not rear door line shadow showing vertically in that area

There is no rear quarter window (as on F20 rear door), that may make the body look fat there.

It is a strange visual trick with hatchbacks (Sporthatch) 5 doors can look lower than a 3 doors