[itsme]

I think (just watching what happens and guessing) the available width of the page (without left and right page margins) is divided into a number of 'boxes' that are equally wide. There's a left and a right column for comments with a number of measures in between. The measures are enclosed in measure bars.
See example post ChordGrid, additional left column - Musikaner https://www.zubersoft.com/mobilesheets/f...12152.html
{start_of_grid 3+4x4+1} divides the page into 20 columns, whereas {start_of_grid 7+4x4+1} makes 24 columns.
{start_of_grid 3+4x4+1}: one measure takes (100/20)*4 = 20 % of the page width, in the PDF opened on my screen it's 42 mm
{start_of_grid 7+4x4+1}: one measure takes (100/24)*4 = 16,66 % of the page width, in the PDF opened on my screen it's 35 mm
That confirms exactly my guess above.
Again: the width of the columns is NOT changed when the font size is changed by my config files, instead chords are placed left aligned in the column where they belong. If the column is not wide enough the chord symbols just overlap.

I think I go one step back and compare the rendering of MobileSheets with the default output of ChordPro without any user config.