Here's the code from my level changes you could tweak;
<!-- lower level requirements on progression -->
<set xpath="/progression/attributes/attribute[starts-with(@name, 'att')]/level_requirements[@level='4']/requirement[@name='PlayerLevel' and @operation='GTE']/@value">8</set>
<set xpath="/progression/attributes/attribute[starts-with(@name, 'att')]/level_requirements[@level='5']/requirement[@name='PlayerLevel' and @operation='GTE']/@value">16</set>
<set xpath="/progression/attributes/attribute[starts-with(@name, 'att')]/level_requirements[@level='6']/requirement[@name='PlayerLevel' and @operation='GTE']/@value">24</set>
<set xpath="/progression/attributes/attribute[starts-with(@name, 'att')]/level_requirements[@level='7']/requirement[@name='PlayerLevel' and @operation='GTE']/@value">32</set>
<set xpath="/progression/attributes/attribute[starts-with(@name, 'att')]/level_requirements[@level='8']/requirement[@name='PlayerLevel' and @operation='GTE']/@value">40</set>
<set xpath="/progression/attributes/attribute[starts-with(@name, 'att')]/level_requirements[@level='9']/requirement[@name='PlayerLevel' and @operation='GTE']/@value">50</set>
<set xpath="/progression/attributes/attribute[starts-with(@name, 'att')]/level_requirements[@level='10']/requirement[@name='PlayerLevel' and @operation='GTE']/@value">60</set>