Hi, 
I was implementing a new financial report that inherit from cash flow report. In this report, I want to get some account.report.line from balance sheet report. After investing the documentation, I found that I need to create account.report.expression. So I used the "aggregation" engine and "cross_report" subformula but I found some difficulties trying to get the same value from the balance sheet report.
Here's the code of cash flow report :

<record id="l10n_tn_bs_cash_flow_report" model="account.report">
        <field name="name">Cash Flow Statement</field>
        <field name="root_report_id" ref="account_reports.cash_flow_report"/>
        <field name="filter_unfold_all" eval="True"/>
        <field name="filter_date_range" eval="False"/>
        <field name="filter_analytic_groupby" eval="True"/>
        <field name="filter_journals" eval="True"/>
        <field name="country_id" ref="base.tn"/>
        <field name="filter_multi_company">selector</field>
        <field name="default_opening_date_filter">today</field>
        <field name="column_ids">
            <record id="l10n_tn_cfr_balance" model="account.report.column">
                <field name="name">Balance</field>
                <field name="expression_label">balance</field>
            </record>
        </field>
        <field name="line_ids">
	​	​	​<record id="l10n_tn_cfr_depreciation_provisions" model="account.report.line">
    <field name="name">Depreciation and provisions</field>
    <field name="code">l10n_tn_cfr_depreciation_provisions</field>
    <field name="foldable" eval="True"/>
    <field name="expression_ids">
        <record id="l10n_tn_cfr_depreciation_provisions_balance"
                model="account.report.expression">
            <field name="label">balance</field>
            <field name="engine">aggregation</field>
            <field name="subformula">cross_report</field>
            <field name="formula">l10n_tn_intangible_assets_depr.balance + l10n_tn_tangible_assets_depr.balance</field>
            <field name="date_scope">from_beginning</field>
        </record>
    </field>
</record>
	​	​</field>
</record>

And here's the code balance sheet report :

<record id="l10n_tn_bs_account_report" model="account.report">
    <field name="name">Balance Sheet</field>
    <field name="root_report_id" ref="account_reports.balance_sheet" />
    <field name="filter_unfold_all" eval="True" />
    <field name="filter_date_range" eval="False" />
    <field name="filter_analytic_groupby" eval="True" />
    <field name="filter_journals" eval="True" />
    <field name="country_id" ref="base.tn" />
    <field name="filter_multi_company">selector</field>
    <field name="column_ids">
        <record id="l10n_tn_bs_column_balance" model="account.report.column">
            <field name="name">Balance</field>
            <field name="expression_label">balance</field>
        </record>
    </field>
    <field name="line_ids">
	​	​<record id="l10n_tn_bs_intangible_assets_depr" model="account.report.line">
                      <field name="name">Less: depreciation</field>
                      <field name="code">l10n_tn_intangible_assets_depr</field>
                      <field name="groupby">account_id</field>
                      <field name="foldable" eval="True" />
                      <field name="account_codes_formula">281 + 291 + 2931</field>
        </record>
	​	​<record id="l10n_tn_bs_tangible_assets_depr" model="account.report.line">
                      <field name="name">Less: depreciation</field>
                      <field name="code">l10n_tn_tangible_assets_depr</field>
                      <field name="groupby">account_id</field>
                      <field name="foldable" eval="True" />
                      <field name="account_codes_formula">282 + 292 + 2932 + 294
	​	​	​	​	​</field>
        </record>
	​ </field>
</record>

And there are the some screen shots of values :

** Balance sheet : Intangible assets depreciation **


** Balance sheet : Tangible assets depreciation **



** Cash flow : Depreciation and provisions **



The value in cash flow should be -126127.240 DT but I'm getting 0.
What I'm doing wrong ?
Thank you.