Working on a new acquirer, I used this views/payment_acqurier.xml

        <record id="acquirer_form_bank" model="ir.ui.view">
            <field name="name">acquirer.form.bank</field>
            <field name="model">payment.acquirer</field>
            <field name="inherit_id" ref="payment.acquirer_form"/>
            <field name="arch" type="xml">
                <xpath expr='//group[@name="acquirer_display"]' position='after'>
                    <group attrs="{'invisible': [('provider', '!=', 'bank')]}">
                        <group>
                            <group>
                                <field name="merchantid"/>
                             </group>
                         </group>
                    </group>
                </xpath>
            </field>
        </record>

Please note the three group containers. If I remove two of them, the views/bank.xml cannot access the field marchantid anymore:

<input type="hidden" name="merchantid" t-att-value="tx_values['merchantid']"/>

So, where do I tell odoo to not travese the xml tree two groups-containers deeper?