I assume that your DB scheme operates on an "integrated" basis with the State Pension. If so, the following example illustrates the logic:
Salary €60,000
State pension €12,000
Pensionable Salary €60,000 less 2 x €12,000 =€36,000
DB Pension 50% x €36,000 = €18,000
Total Pension = € 18,000 + €12,000 = €30,000 (50% x €60,000)
And your contribution should be based on the reduced Pensionable Salary of €36,000 not the €60,000 figure. On that basis your contribution and DB pension are based on the same figure. So I doubt you are over-contributing.