Let’s work through this systematically.

**1. What sector is ENI?**  
ENI is an integrated oil and gas company. The relevant S&P methodology is **Oil And Gas Exploration And Production**, not Regulated Utilities or Transportation Infrastructure. That means the guidelines about regulatory advantage do not apply; instead, competitive position, scale, reserves, efficiency, and financial policy matter.

**2. Current state of hybrid bonds**  
From the data:
- First year of hybrid bond issuance: 2020  
- Issued hybrid bonds in 2021 or 2022: yes  
- The equity movement tables show:  
  - 2020: issuance of perpetual subordinated bonds (€3.0bn)  
  - 2021: another issuance (€2.0bn net)  
  - 2022: coupon payment on perpetual subordinated bonds (€138m), no new issuance but no redemption.  

So hybrids are already in the capital structure, and the previous issuance pattern has been substantial.

**3. Financial metrics**  
- 2022 S&P Net Debt / EBITDA: 0.95x (very low leverage)  
- 2022 S&P FFO / Net Debt: 0.6593 (very strong)  
- Moody’s adjusted leverage trend for 2022: Improving  
- Profitability: 2022 net profit €13.9bn, strong operating cash flow €17.5bn.  

These metrics indicate a very strong credit profile (likely “A” range or strong “BBB+”), with no leverage pressure.

**4. Funding needs and hybrid rationale**  
- Capex in 2022: €7.7bn, largely covered by operating cash flow.  
- No evidence of a transformational M&A program or extraordinary capex that would strain the balance sheet.  
- Refinancing needs appear moderate; the company has solid access to debt markets.  
- The cost of hybrid debt vs senior: Given the sub-senior delta (~0.2% in 2022 over the 10Y swap at ~1.93%), hybrid cost would still be above senior unsecured but not prohibitively high. However, with leverage so low, there is no urgent need to issue hybrids for rating headroom.

**5. Guideline mapping**  
- ENI already has hybrids in its structure (so 0% is unlikely).  
- The metrics suggest **mild leverage optimization** at most.  
- The company’s rating is strong, leverage is falling, and cash generation is excellent.  
- Issuing 7.5%+ would imply meaningful rating headroom constraint, which does not appear to be the case here.  
- A moderate 3.75% could make sense for continued capital structure optimization, maintain hybrid presence, or pre-fund modest needs, but not for distress or downgrade avoidance.

**6. Conclusion**  
Given already-issued hybrids, strong credit metrics, and no significant pressure, the advisable level is at the lower end—sufficient to keep hybrid presence but not aggressively increase it. **3.75%** fits best.

<answer>3.75%</answer>