To determine the appropriate reliance on hybrid bonds for Naturgy Energy Group, we must analyze the company's current financial health, its interest coverage capacity, and the prevailing market environment.

1.  **Financial Position:** As of the end of 2022, Naturgy has a strong net profit of 1,649,000,000 EUR and a significant EBITDA of 4,954,000,000 EUR. Its total equity stands at 9,979,000,000 EUR, while non-current financial liabilities are 13,999,000,000 EUR. The company generated 4,242,000,000 EUR in cash flows from operating activities, demonstrating a robust ability to service its debt.
2.  **Interest Rate Environment:** The provided market data shows a sharp increase in interest rates (Swap Curves 5Y/7Y/10Y and Corporate Bond yields) from 2021 to 2022. The 5Y swap rate moved from -0.264% to 1.726%, and the 10Y swap rate from 0.053% to 1.927%. 
3.  **Capital Structure Strategy:** Hybrid bonds serve as an efficient tool to maintain credit ratings while providing capital flexibility, as they are often treated as equity by rating agencies. However, they are more expensive than senior debt. Given Naturgy's current debt-to-equity ratio and its stable, cash-generative nature (Utility sector), the company should avoid over-leveraging with expensive instruments.
4.  **Conclusion:** A moderate reliance on hybrid instruments (25%) is appropriate for a utility firm of this scale to optimize its capital structure without incurring the excessive costs associated with a higher hybrid mix, especially given the rising interest rate environment of 2022. A 25% allocation allows for the benefits of "equity credit" from rating agencies while keeping the weighted average cost of capital optimized.

<answer>25%</answer>