To assess the appropriate level of hybrid bond issuance for Eni S.p.A., we analyze its financial position as of December 31, 2022:

1.  **Financial Strength and Performance:** Eni demonstrated significant financial improvement in 2022. Revenue from contracts with customers reached approximately €132.5 billion, and profit for the year was approximately €13.96 billion (up from €5.84 billion in 2021). The company maintains a strong cash position, with cash and cash equivalents of €10.16 billion at the start of 2023.
2.  **Capital Structure:** Eni's equity is robust at approximately €55.23 billion. While the company has significant debt (short-term and long-term borrowings), its strong operating cash flows (operating activities generated €17.46 billion in 2022) provide significant flexibility.
3.  **Refinancing and Capex Needs:** Eni is a major integrated energy company with significant ongoing capital intensity (Purchases of PPE amounted to €7.7 billion in 2022). However, it is not facing immediate distress or a liquidity crisis that would necessitate aggressive capital structure optimization to preserve an investment-grade rating.
4.  **Cost of Capital Considerations:** With interest rates rising (as evidenced by the 2022 swap curves), the cost of new debt—and particularly hybrid instruments, which carry a premium over senior debt—will be significantly higher than in previous years. 
5.  **Hybrid Rationale:** Eni already has a history of utilizing perpetual subordinated bonds (equity instruments). Given the company’s strong earnings, healthy cash flow, and solid equity base, there is no immediate, "substantial" requirement to issue hybrids to prevent a downgrade. However, maintaining a moderate degree of rating flexibility is standard for a company of this scale to manage its transition toward energy-related capital projects.

**Conclusion:** Given that Eni is not in a position of "significant leverage pressure" and has strong cash flow generation, a conservative approach is warranted. A 3.75% allocation provides sufficient rating flexibility for moderate funding needs without unnecessarily inflating the interest expense during a period of rising rates.

<answer>3.75%</answer>