Fibonacci is 1 1 2 3 5 8 13... each term being the sum of the previous two. The Golden Mean is much older. For a post-Renaissance view of systems of proportion, consult Modulor by Le Corbusier.
I think we're all agreed that the "too low" effect exists and that there seem to be several ways of coping with it. More than I'd imagined.
If we print digitally, we are using paper with a proportion of 1:sqrt2, the A-series of paper sizes. This might be influencing our thinking on proportions.
And let's not forget that a mount can slip down in the frame, so there can be a physical as well as an optical effect.
Ken, there's no absolute reason why we shouldn't use staples or sticky tape (clear or opaque) to fix a print to the wall. It might be the most valid expression of what we want to say. Not all points can be made by immaculate matting with museum grade board.