The company’s total adjusted capital (debt + equity) is about €17.2 bn.  
S&P’s cap on hybrid equity credit is 15 % of this, i.e., roughly €2.58 bn.  

The perpetual hybrid bonds outstanding are €0.99 bn, which – if treated as 100 % equity‑credit – represent about 38 % of the allowable cap.  
Because the firm is well below the limit, it has room to issue more hybrid debt.  

A prudent target is to use roughly half of the permitted equity‑credit capacity, leaving adequate headroom for future issuance and rating flexibility.  

<answer>50%</answer>