The first of your examples, Ramon, provides a consistent module.
The second alternative doesn’t. This is the same method present before the window muntin issues was corrected. It simply seems like an error to me, I don’t see any use for it.
The best way to create this is probably to research and understand the way Curtain Walls are actually specified in the construction world, how they may differ when they are used as infill glazing panels (where a “frame” MAY be a useful part) as opposed to the entire skin of a building (no frame), and how they differ from Storefront Glazing, which is more properly thought of as Windows (with frames). And to study how AutoCAD Architecture, and Archicad, provide Curtain Walls (for one thing, a differently dimensioned “frame”, isn’t by default a part of the assembly, as I recall.) The measurement from centre to centre of the mullions is more useful to me as a designer, especially in a true curtain wall (where it’s the entire building skin, which doesn’t have a ‘frame’.)