It is possible to put a segmented arch head above a standard window with a niche below the arch, but not to extend the window head up to follow the curve of the underside of the arch.
The standard library has an arched window (and even an eyebrow window) but the centre of the arch cannot be below the window "shoulder".
This type of arched window is common for Victorian/Edwardian buildings in the UK so I often need to model it.
I know one can be made in GDL fairly simply (see image), but is seems an obvious omission from the standard library.