If racquet velocity has normal component only (normal to string bed) and point of contact is sweet spot, you hit pure flat FH (forget about strings actions). Because of the absolute symmetry of the ball there always should be solid contact.
If racquet speed has tangential component only, there never will be solid contact.
Not that simple, because it implies that for any ball, if you want to send it somewhere, you can have the same swing path and the normal component of the force will take care of what you need. That does not happen in practice due to the incoming spin and trajectory of the ball. If you want to send the ball somewhere and it is spinning away, you have to adjust the swing to counteract the topspin, or go with it, depending on what you desire. A ball with no pace and spin needs to be treated differently from one with speed or spin, and the second is not always more difficult, because you can use the incoming pace and spin to advantage. These are the details which the pros handle unconsciously, and are hardly ever discussed in the tennis videos.