<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
       <record id="view_tax_form" model="ir.ui.view">
            <field name="name">account.cresus.mapping.form</field>
            <field name="model">account.tax</field>
            <field name="inherit_id" ref="account.view_tax_form" />
            <field name="arch" type="xml">
                <group string="Refunds" position="after">
                    <group string="Cresus" name="Cresus">
                        <field name="tax_cresus_mapping"/>
                    </group>
                </group>
            </field>
        </record>

        <record id="view_tax_tree" model="ir.ui.view">
            <field name="name">account.tax.tree</field>
            <field name="model">account.tax</field>
            <field name="inherit_id" ref="account.view_tax_tree" />
            <field name="arch" type="xml">
                <field name="description" position="after">
                        <field name="tax_cresus_mapping"/>
                </field>
            </field>
        </record>


    </data>
</openerp>

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data>
       <record id="view_tax_form" model="ir.ui.view">
            <field name="name">account.cresus.mapping.form</field>
            <field name="model">account.tax</field>
            <field name="inherit_id" ref="account.view_tax_form" />
            <field name="arch" type="xml">
                <xpath expr="//field[@name='refund_account_id']" position="after">
                    <group string="Cresus" name="Cresus">
                        <field name="tax_cresus_mapping"/>
                    </group>
                </xpath>
            </field>
        </record>

        <record id="view_tax_tree" model="ir.ui.view">
            <field name="name">account.tax.tree</field>
            <field name="model">account.tax</field>
            <field name="inherit_id" ref="account.view_tax_tree" />
            <field name="arch" type="xml">
                <xpath expr="//field[@name='description']" position="after">
                        <field name="tax_cresus_mapping"/>
                </xpath>
            </field>
        </record>


    </data>
</openerp>

Use xpath for `...position=*>` in xml
[FIX] Use xpath for `...position=*>` in xml
