To determine the appropriate level of hybrid bonds for A2A S.p.A., we must evaluate its financial profile, capital expenditure needs, leverage trajectory, and the cost/benefit of hybrid issuance relative to the guidelines.

1. **Leverage and Financial Metrics**: 
As of Dec 31, 2022, A2A's reported Debt (comprising Other Noncurrent Financial Liabilities of €5.867B and Other Current Financial Liabilities of €1.022B) totals €6.889 billion. Equity stands at €4.467 billion. Total Adjusted Capital is approximately €11.356 billion (Debt + Equity). 
The company's FFO for the year is approximately €1.127 billion (EBITDA €1.505B - Net Interest €90M - Taxes Paid €201M - Adjustments). This results in an FFO to Debt ratio of roughly 16.3%, and a Debt to Capital ratio of approximately 60.6%. These metrics indicate moderate leverage, placing the company in the 'BBB' range. While not in immediate distress, there is limited headroom at the higher end of investment grade, especially considering the rising interest rate environment in 2022.

2. **Capex and Growth Pipeline**:
A2A demonstrates high capex intensity. In 2022, Purchase of Property, Plant, and Equipment was €856M and Purchase of Intangible Assets was €384M, totaling €1.24 billion in organic capex. Additionally, the company spent €497M on obtaining control of subsidiaries (M&A). Total investing cash outflows before disposals exceeded €1.7 billion. While operating cash flow (€1.26B) covers a portion of this, Free Cash Flow (€118M) is very thin, meaning the heavy capex and M&A program is largely debt-funded. This aligns with the criteria for "High capex intensity OR large acquisition pipeline."

3. **Refinancing Needs and Leverage Pressure**:
The company faces significant refinancing needs and leverage pressure. Total debt increased from approximately €5.06B in 2021 to €6.89B in 2022 (a €1.83B increase). Proceeds from borrowings were €4.34B against repayments of €2.78B. Given the ongoing energy transition and infrastructure investments required for an Italian multi-utility, A2A has a sustained high capex trajectory. Without capital structure optimization, the FFO to Debt metrics could weaken further, threatening investment-grade stability.

4. **Cost of Hybrid Impact**:
Looking at the 2022 swap curves (5Y at 1.726%, 7Y at 1.806%, 10Y at 1.927%) and the iShares Euro Corp Bond spreads (1.085%), benchmark yields for A2A (an IG utility) have risen significantly. A hybrid bond would typically offer a slight premium over senior unsecured bonds. However, because the broader cost of debt has already repriced substantially higher in 2022, the incremental spread of a hybrid over the current marginal cost of senior debt is marginal rather than material. Thus, the "cost of hybrid will have a marginal impact on the current cost of debt."

5. **Conclusion on Hybrid Utilization**:
A2A fits the profile for 11.25% utilization: it has high capex intensity and an active acquisition pipeline, faces significant leverage pressure from debt-funded investments, and relies on capital structure optimization to preserve its Investment Grade rating. The cap for equity credit under S&P methodology is 15% of total adjusted capital (€11.356B * 15% = €1.7B). 11.25% equates to roughly €1.27B, a highly manageable amount that falls well within the €3B annual issuance limit and would meaningfully improve adjusted leverage metrics (shifting ~€1.27B from debt to equity equivalents) without overly diluting or costing materially more than senior debt. A full 15% is not warranted as the company is not facing transformational M&A or imminent downgrade risk that requires maximum equity credit support.

<answer>11.25%</answer>