scaling glyphs for tatechuyoko text runs

Below are two examples of half-width glyphs (left) vs. scaled default glyphs (right) in tatechuyoko runs.  The font is Hiragino Mincho ProN, rendered in Firefox on OSX 10.8.  The half-width glyphs are rendered using the OpenType 'hwid' feature.  The scaled glyphs are scaled using the logic "if the combination of letters is more than 1em, scale to 1em".

The first example shows combinations of letters ranked by the width of the default glyphs, from narrow to wide.  The second example shows combinations of digits.