Am 26.03.2011 um 18:15 schrieb Cecil Westerhof:

2011/3/26 Wolfgang Schuster <schuster.wolfgang@googlemail.com>

When you use the “maxwidth” or “maxheight” keys context ignores
the current bodyfont and also the “bodyfont” key to fit the chart on the page.

What is the reason for this? 

Try your example without \startTEXpage/\stopTEXpage and you see that the
chart won’t fit on the page when you set the fontsize to 24pt. To keep the width
of the chart within the allowed width (\textwidth) context reduce the fontsize
until the chart fits.

Wolfgang