To determine the extent to which the company should utilize hybrid bonds relative to S&P Global Ratings' cap, we evaluate the cost of hybrid bonds compared to the cost of equity to optimize the Weighted Average Cost of Capital (WACC). 

S&P limits the equity credit on hybrids to a maximum of 15% of Total Adjusted Capital (TAC), which is the sum of total debt and equity. Up to this 15% cap, hybrid bonds receive 50% equity credit, functioning effectively as cheaper equity.

Based on the 2022 market data provided:
1. **Cost of Senior Debt:** The iShares Core Euro Corp Bond yield is 1.085%.
2. **Cost of Hybrid Debt:** The Sub-Senior Delta for iBoxx EUR Non-Financial IG is 2.295%. This puts the approximate yield on hybrid (subordinated) debt at 1.085% + 2.295% = 3.380%.
3. **Cost of Equity:** Using the 10-year swap rate (1.927%) as the risk-free rate and adding a standard equity risk premium scaled by the beta of a utility company like HERA S.P.A., the cost of equity confidently exceeds 5% to 6%.

Because the cost of hybrid bonds (3.380%) is substantially lower than the cost of equity, it is highly accretive for the company to replace common equity with hybrid debt. It provides partial equity credit to maintain credit ratings while lowering the overall WACC. 

However, any hybrid issuance beyond S&P's 15% limit is treated as 100% debt by rating agencies, meaning there is no longer a rating benefit to issuing these more expensive debt instruments compared to standard senior debt. Therefore, to minimize its overall cost of capital while maximizing rating agencies' equity credit, the company should perfectly max out this allowance, fully utilizing the cap.

<answer>100%</answer>