The ResMed Quattro FX full-face CPAP mask with headgear was created in such a way as to minimize patient inconvenience without sacrificing the quality of CPAP therapy. For this reason it has no forehead strap that can get in the way and leave annoying markings on the forehead. This also means that you have clear sightlines.
The cushioning system is designed to make use of an air suspension. This allows the cushion to work to maintain a seal with the face as the frame shifts around when you move. This is part of the reason why the ResMed Quattro FX full-face CPAP mask with headgear does not require a forehead strap. It also means that even as you move around the pressure of the mask against your face is spread out to prevent pressure points.
As with all Mirage series CPAP masks, this one makes use of a dual-wall cushioning system to balance fit and feel. One layer works to keep the mask in place while the other layer works to keep a soft, comfortable seal against your skin. The soft outer layer means that you don't suffer from markings or skin irritation. The firmer inner layer means that you get some stability. All of it is air suspended.
Once you've sized this mask and headgear appropriately, putting it on and forming a good seal is just a matter of swinging the mask onto your face. The cushioning system aids this. You start with the nasal cushion on the nose and then swing it into place. The air pressure takes care of sealing it up as the cushions inflate to take a gentle hold of your face. No headgear tightening is required.
So getting the right fit and putting the mask firmly in place is a simple matter. It is little more than putting the cushion on your nose and swinging the mask down into place before before placing the headgear clips.