I just posed the same question for my 2019 Hatch.
"Hello, 2019 Impreza Hatch. One month old. I like it. Hauls my bike well. I lifted up rear floorboard and stowed rear cargo cover . I do not need it for now.
It does not go deep enough on the floor beside tire, so when rear cover board is re-stalled, rear cover board is no longer completely flat.
Is that the way it is supposed to be or am I missing something real simple? Thanks."
Maybe that is the way it is supposed to be on these 2017 and up Hatchbacks.