To determine the appropriate reliance on hybrid bonds for TenneT Holding B.V., we analyze the company's financial position and the market environment as of the end of 2022:

1.  **Capital Structure Composition**: TenneT’s total equity as of 2023-01-01 is 7,713,000,000 EUR, of which 2,125,000,000 EUR is classified as Hybrid Capital. This represents approximately 27.5% of the total equity (excluding liabilities).
2.  **Profitability and Risk**: The company reported a significant operating loss of 976,000,000 EUR and a net loss of 879,000,000 EUR in 2022. Operating expenses have risen sharply (from 5.86 billion to 9.39 billion), and the company is heavily reliant on capital-intensive investments (4.42 billion in asset purchases).
3.  **Market Environment**: The swap curves and bond spreads (e.g., iBoxx EUR Non-Financial IG) show a significant increase in financing costs in 2022 (e.g., the 10Y swap rate moved from 0.053% in 2021 to 1.927% in 2022). Higher interest rate environments generally make traditional debt more expensive, which might suggest a benefit to hybrid capital to maintain credit ratings.
4.  **Strategic Reliance**: Given TenneT is a transmission system operator (TSO) owned by the Dutch State, it requires stable, long-term funding. While the current 27.5% is close to a 25% allocation, the combination of substantial losses and the need to maintain a strong balance sheet for massive infrastructure investment suggests a conservative approach. However, moving to 50% or higher would significantly dilute the equity base and increase the cost of capital, as hybrid coupons are typically higher than senior debt. Maintaining a level close to the current actuals—roughly 25%—balances the need for equity-like credit treatment with the cost of capital.

Given the current balance sheet structure and the fiscal performance, maintaining a reliance near the current levels is most prudent.

<answer>25%</answer>