First, as to lamp shades:

Ask your GF. Do you know, there are actually specialist shops for that sort of thing? There was even one right here in Bergen, Norway (pop. 250 000) until a few years ago! I'm pretty sure it should be fairly easy to turn up lampshade "skeletons" and patterns, too...

And then print/matting/frame sizes.

I've been thinking about this for years, and here's some of my thoughts:

There seems to be some sort of mathematical relationship which describes the optimum print size for any given image. Some images show a definite shift of focus with changing size, but these are rare. A good example is my "Commercial Bank of ...", in my personal gallery here. At sizes up to about 8x10" the main subject is the bank building, at a size of 16x20" the focus shifts to the small group of people in front of the building. I have not made even larger prints to see what would happen.

The main variable seems to be what I call "Smallest Significant Detail", or SSD for short. I have chosen this term with an emphasis on "Significant" - it doesn't have to be either small or detailed. I just can't come up with a better term (yet).

As the so called "normal" viewing distance is dependent on the size of hte print, it is obvious that this does not enter into it. Instead, I have come to believe in a "standard" viewing distance of around 80cm (about 2' 8") instead, which in most cases is a comfprtable distance to view a picture. You would move closer for a close scrutiny or step back for an overview, but just look at people in galleries...

Now, a very large picture seen from this distance can either include a lot of "background" making the SSD about 10-20 cm (4"-8") big, or show a pronounced "poster effect". The poster effect is what makes viewers back across the room to get to a "safe distance"... Smaller pictures will have relatively larger SSD compared to the image size, or the perception may shift.

The SSD can be just about anything: In a portrait, it will be the face; in figure, a body; in landscapes, a tree... This is possibly the key to making a picture "work" at any size print. Returning again to the bank picture example, we see the perceived SSD changing from a building to a group of people simply by changing the size of the print. I wouldn't be surprised if the SSD would change to a single person (the white-clad one) with even larger print size!

So how does matting influence this?

The matting functions as something between background and frame, with some elements of both. A wide matte can influence the perception of the SSD - or rather the selection of it. In extreme cases it defines the entire image as SSD, and invites a very close scrutiny of that small rectangle. At the other extreme, an unmatted print in the same size frame would imply that most of the picture is "background".

And that, in my opinion, is a very short summary of why some ictures need to be big, some small, some matted with wide margins, some with hardly any, and a very few images can work regardless. But those last ones are so rare that I can't remember ever having seen one.