I've had this happen a few times where a zed will launch at me from outside a building- typically when it's spotted me downstairs and I've run upstairs in a two story building. I will stay in the room upstairs waiting for it and it will start hitting me from out of view downstairs.

On occasion this can happen with zeds in a crawl space while I am on the main floor of any building. They appear to "wade" through the floor usually after having entered by transitioning through a wall (if all doors are closed.) In most of the cases I've experienced however I have not closed the door so they come in downstairs directly underneath where I'm standing and just start flailing. They hit me at least one floor above- I have not tested whether or not they can still hit me if I'm 3 floors above them (or more).