Perhaps what AndyS is saying is that, if the sidelights are positioned at the top of the bottom aperture, with the indicators below then you can't achieve the 'angles of visibility' speciied in table 1. Which in my version of the doc, seems to be 15deg above/below the horizontal, or 5deg above/below hori for sidelights in the height band 250mm to 750mm?
So rather than be a direct IVA requirement, the design of the 40's apertures means that you end-up having to put the sidelights in the headlamp unit, to pass the vis angles?
Keith