Is the horse dead??? I seem to keep flogging it. Yes. Another update.
Since the Ceiling fcn seems to be working correctly, and the goal is to have the shape increment in steps of page grid spacing, then, a further simplification is possible and along with relocating the formula, using SETATREF fcns, to the width cell. I set minimum width = 4 mm. Within the shapesheet, in the User Section, Prompt cell, there is, for convenience, a method to change the grid spacing. Note, vert grid = horiz grid. Also, for my convenience, shape height = shape width.
As user changes the size of the shape, it will only increment to multiples of the page grid.
Enjoy!