To determine the appropriate level of hybrid bond issuance, we first compute the company’s total adjusted capital, defined as debt plus equity. Using the 2023 balance‑sheet data:

- Total equity (including non‑controlling interests) = €2,054,682,000  
- Financial debt (including lease liabilities, borrowings, and other interest‑bearing liabilities) = €2,374,932,000  

Total adjusted capital = €2,054,682,000 + €2,374,932,000 = €4,429,614,000.

S&P Global Ratings caps the equity credit on hybrids at 15 % of total adjusted capital:

15 % × €4,429,614,000 = €664,442,100.

Thus, the maximum amount of hybrid bonds that can receive full equity credit is €664.4 million, which corresponds to 15 % of total adjusted capital. Since the cap is expressed as a proportion of the total adjusted capital, the company can utilize up to the full cap (i.e., 100 % of the allowed equity credit). Therefore, the company should aim to use hybrid bonds at the maximum level permitted by the rating agency’s limit.

<answer>100%</answer>