I know that for the most part you want to stack your magnifier and red dot as close as possible, but is there anything intrinsically wrong if you leave a small gap?

I ask in relation to this setup.



The magnifier shown will be shared between two rifles. The other is mounted much closer, but because I want to preserve the down flip cap on this sight I tried sighting through it as pictured and I don’t see any issues. It still magnifies it fine, and I don’t get any shadowing around the outer edge. Besides the fact that it leaves a space for something to get between the magnifier and red dot, will it cause any problems?

I see no problem. I've had mine mounted both ways and had no issues with sighting or distortion.