Fortum Oyj's financial situation at the end of 2022 shows significant volatility and distress. Key observations include a massive net loss of 10.29 billion EUR, driven largely by discontinued operations (-11.3 billion EUR). The company's cash position dropped from 7.59 billion EUR to 3.92 billion EUR, while its total equity decreased sharply from 13.67 billion EUR to 7.74 billion EUR. The company's leverage and risk profile are further underscored by high interest expenses and significant negative cash flows from operations.

Market data for 2022 indicates a sharp rise in interest rates (e.g., the 10Y swap curve moved from an average of 0.053% in 2021 to 1.927% in 2022, and corporate bond spreads also widened). Relying on hybrid bonds (which act as equity-like instruments with higher coupon costs and subordinated ranking) provides a buffer to the balance sheet and avoids further dilution of existing equity while offering tax-deductible interest payments in many jurisdictions. However, given the already high level of financial risk, a "comparable operating profit" of 1.87 billion EUR, and the need to restore a solid credit profile, a 25% reliance on hybrid bonds in the capital structure is a prudent balance between maintaining flexibility and managing cost of capital, whereas higher levels might exacerbate the already elevated financing costs under the current interest rate environment.

<answer>25%</answer>