FVWM: SnapGrid offset?

I have a custom function to move icons:

    DestroyFunc MoveIcon
    AddToFunc MoveIcon

    # Set icons to snap to grid exlusively
    + I WindowStyle SnapAttraction 0
    + I WindowStyle SnapGrid $[ICONWIDTH] $[ICONHEIGHT]
    + I UpdateStyles
    + I Move

    # Reset snap settings for normal windows
    + I WindowStyle SnapGrid 0 0
    + I WindowStyle SnapAttraction $[SNAPPROXIMITY] Windows Screen

This allows me to snap icons into a grid while moving them,

Recently I decided to right-align my icons along the screen instead of left. But since my screen resolution is not a multiple of $[ICONWIDTH], the above function now snaps the icons slightly off the screen while moving them along the right edge.

It appears the SnapGrid is anchored at 0, 0. Is there a way to provide an offset? I don't want to change my grid size, just the offset of where the grid is anchored.

╰─> fvwm --version
fvwm 2.7.0 compiled on Sep  8 2024 at 19:34:08
with support for: ReadLine, RPlay, Stroke, XPM, SVG, Shape, XShm, SM, Bidi text, Xinerama, XRender, XCursor, XFT, NLS

Thanks,

Stephen