I have deep set eyes so my cups are at the first stop and sometimes I just keep them all the way down and rest them on my brow with a slight tuck of my chin. I adjust for ipd by squeezing the bin's until I can maximize fov and have no distortion when looking center frame. There's a sharp black circle if it's correctly adjusted, otherwise it's a soft circle with a loss of FOV. I can even pan well with them, but as soon as my eyeballs stray to about 2/3rds away from center glass I get black out and I even get vignetting before that. They're not unusable. In fact, I really like them! I just think if I'm paying all this money for glass I should probably put it towards a pair that works better for my face.
I'm hoping the 8x40 SFL will work better for my face. My thinking is that the extra light will help reduce the black out. I have Monarch 7 8x42 and 10x42 and I get vignetting with them as well, but only blackout when I'm shifting my eyes to the extreme edges.
I'm assuming binoculars exist where you can put your face up to them and scan all the edges of the glass without vignetting and blackout but I don't know...