the rock drawing on the right is a photo of a suburb I think the flare adds a nice easy addition to a layer for its extra sense of depth that follows analogue logic
I do see that it helped on the other ones, Ian. So it seems that there can be nothing that always helps, even if applied to the most similar situations. Very strange to me, really.
But highly developed image! And that's quite intriguing as it shows that the highly developed can (must?) be based on the primitive - in the sense of the simple, seld-contained, clear, irreducible principle. Much like constructing mathematics out of such "primitive" ideas like for example points, numbers, and so on. (OK, I admit that I just *had* to say that ;-))
But for me, and without wanting to deny the flare as a producer of depth, there is also another depth supplier here. The hue/light/geometry difference of the left and the right parts of the image. The look and feel of both is quite similar, but the more specific properties aren't. I seem to perceive the left part nearer to my eye than the right part, without really knowing if this is subjective. Still I think that this together with the fact, that the "sphere" is only partially on image (near me) while the "rectangle" is captured as a whole (far from me), makes the depth perceivable.
Could a sharp focus, at least on some part, make it even stronger in its depth?