Fabrice Couvreur
19. Juli 2016 um 15:19
The third column of matrix is not centered vertically and horizontally.

Add the following two lines to your example

    \setupformula      [option=frame]

and you can see the third matrix isn’t centered (the small gab on the left side is the cell offset)
because it’s too wide for the cell.

BTW: It’s good style to end *each* matrix line with \NR.