In CWB the unit fires into a box the line set by the unit firing. The shooting box as described on page 86, the box shows ranges of 4" and 10".

When the artillery is attached the shooting would include the artillery and increase the box width and ranges to include the artillery base, so in the diagram the box is shown as 90mm wide, this width will increase to 130mm. With ranges you will still have the short range 4" line, the long range 10" line but you will now have the Ranges on page 89 for artillery added. So the box will go out to 30 or 40 inches, but that is just for the artillery not the infantry weapons. So you will ignore the normal base described angles for the shooting arc.