Your builder was just giving a simplistic explanation of the coverage of the lens, which can vary with the construction of the lens. If you were using the same lens in a view camera shooting landscapes you would most likely have about half the coverage, shooting 1:1 increases your coverage ability with any given lens. If you want a really good technical book on the subject of view cameras try Leslie Stroebels book View Camera Technique. That will get into the subject of coverage of various lens designs as well. The length of the lens barrel of any focal length lens has a large effect on the covering power as well as stopping down the aperture. J.L. Woodens Large Format Optical Reference Manual gives very specific details on lens specifications.