I have to start out by saying a lot of forms of boxes are not easy to make cameras out of. Almost any kind of one piece box with a fold down lid with a tab that inserts into the front are going to be almost impossible to make light-proof without taping over part of where the top closes when you put the paper in. I really don't like cameras that need to be sealed with tape every time you load them. Paper boxes especially are going to get damaged removing tape.
Also boxes that are not very stiff and don't fit tightly into the lid, or distort somewhat when you place the lid on are going to be prone to light leaks.
The best boxes are those which are fairly rigid cardstock and have the lid which is just as tall as the interior. My favorite lately are Oaks Candy Boxes.
The one on the left is the one pound and on the right is the two pound.
The cardstock is white which is always a little suspect for opacity, but with a layer of flat black paint they were completely light-proof. Notice that I painted the bottom not only on the inside, but also on the outside, so where they're together, the joint between them is black on both sides. You want to make it as hard as possible for the sun to sneak in.
The one pound box is 4 x 8 inches and the two pound is 5 x 10 inches. They're both two inches deep, so they're pretty wide angle for these image sizes.
Here's the image from the two pound box,
One aspect of wide image formats with short distances to the pinhole that's obvious here is vignetting. With lenses this term usually refers to part of the image being shadowed by part of the opening, but with pinhole it more commonly refers to the fact that there's a significant exposure gradient toward the edges of the image. In a wide box like this the edges of the paper are quite a bit farther away from the pinhole than the center is. The amount of light a lens or pinhole transmits is generally indicated by it's f ratio: focal length divided by the size of the opening. The larger the number, the less light it transmits. Focal length is an inappropriate term for pinhole because there's no focusing going on, but I'll use it for simplicity's sake. In pinhole the distance from the pinhole to the paper gives the same sort of geometric results as focal length of a lens does.
I used a half millimeter pinhole, so the two pound box, at a point directly under the pinhole, is f100 (50mm/.5mm). The right and left edges of the paper are almost six inches (152mm) away from the pinhole and therefore f305. Thats nine times less light reaching the paper. In addition, from that perspective, the pinhole becomes a foreshortened ellipse reducing it's area and reducing the amount of light even more. The end result is that the picture fades to black before it reaches the edge. We could argue whether that's good or bad – some people like it and some don't.
It also exhibits a characteristic of all wide angle objectives. Perspective is stretched out so things seem farther away from the camera and each other than they appear to your eye. To get this picture I had the tripod in the middle of the street and had to cut short the exposure when an SUV unexpected came around the corner. It's always a good idea to get closer than you think you need to with a really wide angle camera
Oaks has a big sign in their store that says they don't sell empty boxes with the Oaks branding already printed on them, so my wife and I made the sacrifice and ate the candy so I could make the cameras to show you.