I have a Peterson 315 System Std P-Lip. Can the P-Lip stem just be swapped out for a fishtail? Smokingpipes.com sells P-lip replacements (out of stock) but mentions, "P-Lip and fishtail stems feature a different taper to their bases, for best fit a P-Lip or fishtail stem should be replaced with one of the same style". I'm confused, does that mean a pipe sold with a P-Lip is built different than a pipe sold with a Fishtail?