Hi Peter,
You have to work it back so the tang slips into the ram rod groove and is fully inlet. Fortunately, the extension or tang is tapered so you can move it back ward without creating gaps but it is a bit of a pain. Try to maintain as much wood as you can so you have sufficient for the rivet that holds the cap in place. One aid is a paper pattern. Wrap paper around the nose cap and trace the outline. Then cut it out and wrap it around the stock and trace the outine on the stock. That will give you an idea how far the tang will go back so you can remove wood for it. Just remove wood shy of your outline on the stock to allow for close fitting.
dave