have you tried
\externalfigure[./1/fig.1] ?
Good thought, although it also did not work. The behavior very strange because the subdirectory specification sort of works if the figure name is 1/fig.2 but not if it is 1/fig.1 or 1/fig.3. I say 'sort of' because it finds the figure and gets the dimensions from the .rli file it makes, but it doesn't include the figure in the PDF. I'm trying \tracingall to see whether I can find what goes wrong.
Another option is to add the directory to the search path and not to use directories in the name.
\setupexternalfigures[directory={% ./1,% ./2,% ../whatever/include}]
Thanks, that works reliably. -Sanjoy `If we are fortunate, Republicans will complete their self-destruction before they extinguish the Constitution and destroy America.' --Paul Roberts, former assistant Treasury Secretary under Reagan