And to kind of carry on JQ's comments, make sure you have the right size cushion. The nice thing about the Simplus is the fact that size changes require only changing the cushion, not the whole mask. Here's the sizing guide, courtesy of CPAP.com, not the best, but...
Size. The top of the mask should be about eye level and the bottom fall into the indentation between the chin and lips. The right size should feel like it fits naturally.
To get an idea of how the mask should be tightened, lie down with the mask to the face under pressure, but without the headgear attached. It should only take gentle pressure from your fingers to seat it and stop it from leaking (if it is the right size). This, then, is the same pressure the straps should apply when attached.
Sometimes people's chin will drop so much in deep sleep that it will fall out of the bottom of the mask, or nearly so, and cause leaks. One way to prevent that is to take a strip of soft cloth about an inch wide and 18 inches long, or so, place it under the chin, up between the face and the lower straps of the mask, and back down under the chin to tie. This works kind of like a chin strap, but the purpose is not to keep the mouth closed, but just to prevent the jaw from dropping too far. It should not be tight, just snug with the mask on and the mouth partly open as it would be normally. A strip cut from an old t-shirt, maybe.
Most of these FFM use an "air cushion" to fit, so the edge of the mask has to be allowed to inflate to seal. That's why too tight doesn't work. Often the masks can be seated by gently pulling them straight out from the face while being worn and under pressure to allow the seal to inflate and then letting them settle back to the face.
As JQ mentioned, the "mask fit" feature is helpful to test that the mask won't leak under higher therapy .
You should consult with your provider if you feel your pressure settings are disturbing you sleep.
