Closer inspection of the above two RWS reveals measurable differences in letter heights. The top strip has letters that all measure 9mm, while the bottom strip appears to have a mix of 9mm and 10mm letters.  In fact, the bottom strip has lettering that follows the pattern:

      MONONGAHELA VALLEY / COUNCIL / PENNSYLVANIA

where larger letters in bold represent the 10mm letters.

Both patches examined were mint, so shrinkage was not a factor affecting the dimensions of the patches.  Measurements of the two patches are:

        9mm variety:  109/40/72, overall width 129, height 41
      10mm variety:  112/41/73, overall width 131, height 42

There was also a slight difference in the shade of the twill, with the 9mm variety being slightly lighter than the 10mm variety.