Acciona S.A. operates in capital-intensive sectors (infrastructure and renewable energy) that require long-term project financing. Reviewing the 2022 financial data:

1.  **Capital Structure:** The company has a significant and growing presence of "Participaciones Preferentes, Obligaciones y Otros Valores Negociables" (Hybrid/Debt instruments). As of 2023-01-01, these items on the non-current side amount to 3,101 million EUR, compared to 2,624 million EUR in standard non-current loans.
2.  **Market Environment:** The provided market data shows a sharp increase in interest rates for both 5Y and 10Y swaps, with the 10Y swap average moving from 0.053% in 2021 to 1.927% in 2022. Additionally, the IBOXX EUR Non-Financial IG spread (Sub-Sen) widened from 1.298% to 2.295%.
3.  **Rationale:** Hybrids are often used by capital-intensive firms to manage credit ratings and maintain financial flexibility while financing long-duration assets. However, excessive reliance on hybrids increases interest coverage risk, especially in a rising rate environment (as observed in 2022). Acciona's current debt structure shows a high reliance on these instruments (already roughly 50% of its non-current financing debt). Given the current inflationary and rising interest rate environment, maintaining a moderate balance (50%) is prudent to balance tax-deductible debt costs with the equity-like features of hybrids, which protect the credit rating. Moving higher would subject the company to higher refinancing costs, while moving lower would significantly increase the burden on standard debt and equity. A 50% allocation reflects a balanced capital structure appropriate for the firm's specific industry and current macro-financial profile.

<answer>50%</answer>