The lenses are designed for your eyes to be as close as possible to them. Then the sweet spot will be adequate. If you see vignetting on one edge only you need to shift the headset up/down or side/side not in/out. Look straight up, adjust the straps with the headset in the sweet spot then when looking around it should stay there. It needs to be worn pretty tight. It took me over a week of daily hour long use to finally figure all this out. If you see slight vignetting on all sides you might just have it perfect, try to immerse yourself in the sim and you'll stop noticing it.