preceding axis is too permissive for my stylesheet

xsl processor: Saxon 8B
xsl version 2.0

Here is my test case:

<?xml version="1.0" encoding="UTF-8"?>
<root>
    <div1><!--Article-->
        <ptr target="ids.27.3.1fm" n="10"/>
        <ptr target="ids.27.3.2fm" n="11"/>
        <div2><!--Subsection-->
            <ptr target="ids.27.3.3fm" n="12"/>
            <ptr target="ids.27.3.4fm" n="13"/>
        </div2>
        <div2><!--Notes-->
            <ptr target="ids.27.3.1tm" n="10"/>
            <ptr target="ids.27.3.2tm" n="11"/>
            <ptr target="ids.27.3.3tm" n="12"/>
            <ptr target="ids.27.3.4tm" n="13"/>
        </div2>
    </div1>
    <div1><!--Article-->
        <ptr target="ids.27.3.3fm" n="14"/>
        <ptr target="ids.27.3.4fm" n="15"/>
        <div2><!--Notes-->
            <ptr target="ids.27.3.3tm" n="14"/>
            <ptr target="ids.27.3.4tm" n="15"/>
        </div2>
    </div1>
    <test><ptr/></test>
</root>

Here's my stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="2.0">
    <xsl:output method="xml" indent="no" encoding="utf-8" media-type="text/xml"
        doctype-public="-//TEI P4//DTD Main Document Type//EN"/>

    <xsl:template match="@*|node()">
        <xsl:copy>
            <xsl:apply-templates select="@*|node()"/>
        </xsl:copy>
    </xsl:template>

    <xsl:template
match="ptr[matches(@target,'([a-z]{3})\.([0-9]+)\.([0-9s]+)\.([0-9]+)[tf]m+?')]">
        <xsl:choose>
            <xsl:when
test="matches(@target,'([a-z]{3})\.([0-9]+)\.([0-9s]+)\.([0-9]+)[f]m+?')">
                <ptr target="{@target}" n="{count(.|preceding::ptr)}"/>
            </xsl:when>
            <xsl:otherwise>
                <ptr target="{@target}" n="{count(.|preceding-sibling::ptr)}"/>
            </xsl:otherwise>
        </xsl:choose>

    </xsl:template>


For my output, I get:

<?xml version="1.0" encoding="utf-8"?><root>
    <div1><!--Article-->
        <ptr target="ids.27.3.1fm" n="1"/>
        <ptr target="ids.27.3.2fm" n="2"/>
        <div2><!--Subsection-->
            <ptr target="ids.27.3.3fm" n="3"/>
            <ptr target="ids.27.3.4fm" n="4"/>
        </div2>
        <div2><!--Notes-->
            <ptr target="ids.27.3.1tm" n="1"/>
            <ptr target="ids.27.3.2tm" n="2"/>
            <ptr target="ids.27.3.3tm" n="3"/>
            <ptr target="ids.27.3.4tm" n="4"/>
        </div2>
    </div1>
    <div1><!--Article-->
        <ptr target="ids.27.3.3fm" n="9"/>
        <ptr target="ids.27.3.4fm" n="10"/>
        <div2><!--Notes-->
            <ptr target="ids.27.3.3tm" n="1"/>
            <ptr target="ids.27.3.4tm" n="2"/>
        </div2>
    </div1>
    <test><ptr/></test>

This not quite what I want. In the second <div1>, I want the first two
@n values to be "1" and then "2", to match the markers in "Notes". The
preceding axis is too permissive, and preceding-sibling doesn't get me
there either, since for what I want, it doesn't track how @target
values with an "fm" in them are nested. I'm stumped. Any suggestions?
This list has been a great resource for me. I really appreciate your
help and attention!
Tony