Concerning the "natural" viewing perspective, perhaps the simplest way to naturally force the viewer to place him/herself at the correct distance is to contact print (???).... these massive enlargements (which seem to be all the rage now) just push people back, it seems to me. Contacts tend to cause people to view them at arms' length.
How about this: when you go to a movie, where do you prefer to sit? Some folks like to sit right up front so that they are turning their heads to take in the scene. I did that once and actually felt a bit ...dizzy... after a while, but indeed one does feel "part of" the scene. Especially if the screen is curved (IMAX).
I suppose this theory of natural viewing perspective perhaps doesn't take into account the neck muscles. A reasonable question might be whether one wants to take in the whole scene at once, or rather look around through it, exploratively, from left to right. There is nothing "unnatural" about that last option- we do look around when we view actual scenes in the real world, no? That becomes a bigger issue with pano aspect ratios, of course. I find that squares satisfy me the most, personally, because of the equal weighting of the whole, which causes me to think of it as a Whole rather than a collection of sub-subjects. Panos, which I admit that I am just now starting with, force an entirely different way of seeing.