account-financial-reporting/account_financial_report_horizontal/data/report_paperformat.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>
        <record id="paperformat_euro_landscape" model="report.paperformat">
            <field name="name">European A4 (Landscape)</field>
            <field name="format">A4</field>
            <field name="page_height">0</field>
            <field name="page_width">0</field>
            <field name="orientation">Landscape</field>
            <field name="margin_top">40</field>
            <field name="margin_bottom">23</field>
            <field name="margin_left">7</field>
            <field name="margin_right">7</field>
            <field name="header_line" eval="False" />
            <field name="header_spacing">35</field>
            <field name="dpi">90</field>
        </record>
</odoo>