That's exactly it. You have to bring the "copy" of the left side to overlap with the "original" right side. Then move forward/backward until the overlapped 2 come into focus. The shimmering should stick out, was so shocking when it finally clicked for me.

I used put my finger halfway to the object, look at my finger until the crossed images in the background converge, then remove my finger and let my eyes stay in the same spot.

Now I can do it without the finger.

> until the crossed images in the background converge

that's the issue! like an OP i never was able to "converge" the images. for me it is phisically impossible: they are too far apart and never come closer. maybe because i have an astigmatism.