Ken,
With Scale, what you doing is "effectively cropping" with the Frame Size. The Frame Size is like the aperture in a photographic matte - the aperture stays the same, but if you put a photograph, that is larger behind it, you still only see that aperture, and what shows through it. Think of a matte with an 8 x 10 aperture cut into it. If you place an 8 x 10 photograph behind it, you see the entire photograph. If, however, you enlarge that photograph, to say 11 x 14, it is larger but still only showing the area of the 8 x 10 aperture.
Hunt