Obviously, the larger the area covered on a map, the less detail can be dedicated to it. By the same token, the less area covered, the more detail you can find for it. The most detailed map series of the entire U.S. is the USGS 7.5 minute topographic map series. This series shows large amounts of detail over a small area. Large scale means Small area covered by the map.
Small scale means Large area covered by the map.
The size of the sheet has nothing to do with determining scale. There are many variations, but there are three types of projection methods on which all others are based. Each method distorts the globe in different fashion, but, as with any attempt to flatten around surface, they do distort. Conical projections offer less distortion in the Mid-Latitudes while a cylindrical projection distorts less around the Great Circle lines. Azimuthal, being based on a flat plain, distorts more and more as you move from the center.