I have a Primary Arms magnifier, with flip to side mount, for my 15-22. I have it positioned as far back on the rail as possible, so much so that I removed my MBUS to allow it to get as close to me as possible. My optic is positioned accordingly, which puts it a little more forward than I would choose if I didn't have the magnifier. However as mentioned above, it most certainly stays on the receiver... not the guard. Also as mentioned, that forward position gives me a better field of view, which is nice when acquiring the next target.
Even though the magnifier can flip to the side, for normal shooting I have it removed. I prefer keeping my gun as light and clean as possible and for the shooting I normally do, magnification is not needed... nor is the extra weight. But by keeping my optic where it is, I retain the flexibility to instantly add back the magnifier, when needed.
Don't forget you have an adjustable stock on the gun (assuming you don't live in a communist state). I think some folks forget about that feature. If my magnifier is removed and I wish my optic closer to me, as opposed to moving the optic, I simply shorten the stock. You can bring your eye to the optic as opposed to moving the optic back on the rail.