To determine the optimal reliance on hybrid bonds for Bouygues, we must evaluate the company's leverage, interest coverage, and cost of capital, comparing the need for equity-like credit from rating agencies against the additional cost of subordinated debt.

1. **Leverage and Debt Capacity**: 
   At the end of 2022, Bouygues had a Net Debt of €7.44 billion and Total Equity of €13.93 billion. 
   To calculate EBITDA, we can take the Profit/Loss from Operating Activities (€1.87 billion) and add back Depreciation and Amortization expenses (€2.22 billion) and Depreciation of Right-of-Use Assets (€0.44 billion), yielding an approximate EBITDA of €4.53 billion. 
   This puts Bouygues' Net Debt-to-EBITDA ratio at roughly 1.6x. This is a conservative, low-leverage profile, comfortably within strong Investment Grade (IG) parameters.

2. **Interest Coverage**:
   With an Operating Profit of €1.87 billion and an Interest Expense of €231 million, the interest coverage ratio is strong at over 8.0x. This indicates that the company has no difficulty servicing its current debt load.

3. **Cost of Debt**:
   The provided market data indicates that senior corporate bond yields (approximated by the iShares Core Euro Corp Bond index) averaged 1.085% in 2022. The Subordinated-Senior yield delta for iBoxx EUR Non-Financial IG bonds was 2.295% in 2022. This demonstrates a substantial premium required to issue hybrid (subordinated) debt compared to senior debt. 

**Conclusion**: 
Hybrid bonds are typically issued by non-financial corporations to defend their credit ratings when their leverage approaches or exceeds rating agency thresholds for their current band, as hybrids receive partial equity credit. Since Bouygues has strong interest coverage, low leverage (Net Debt/EBITDA < 2.0x), and substantial cash flows, the company maintains significant borrowing capacity. Issuing hybrid debt would force the company to pay an unnecessary yield premium (approximately 2.3% above senior debt) without providing a required strategic benefit. Therefore, the company's capital structure should rely 0% on hybrid bonds.

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