Based on ENGIE's profile as a large regulated utility with significant capex (≈€6.4 bn/year), a sizable current‑debt maturity (≈€12.5 bn due within one year) and moderate leverage (net debt/EBITDA ≈2.4×, FFO/debt ≈21%), the company faces moderate refinancing and funding needs. Its existing hybrid instruments (deeply subordinated perpetual notes of ≈€3.4 bn, representing ~4.25% of total adjusted capital) provide a base, but further hybrid issuance would help:

* Maintain equity credit and improve adjusted leverage metrics, preserving the 'A'‑range rating;
* Provide flexibility to fund high capex without excessive senior‑debt issuance;
* Slightly increase the cost of debt (hybrid yields are modestly above senior debt) but the benefit outweighs the marginal cost.

The 7.5% target aligns with the guideline for “moderate refinancing or acquisition needs, rating headroom moderately constrained, hybrid issuance meaningfully improves adjusted leverage metrics” and stays within the annual issuance cap (≈€2.6 bn incremental hybrid would be needed to reach 7.5% of TAC, well under the €3 bn/year limit).

Higher options (11.25% or 15%) would exceed the permissible issuance volume and are not warranted given the company's manageable leverage and no transformative M&A pipeline.

<answer>7.5%</answer>