I think we're on the same page here, just coming at it from different angles - your figures are correct. As things stand a public servant gets 50% of salary including COAP, but not 50% of salary plus COAP.
The point I'm trying to make is that while a defined benefit scheme can be coordinated, a defined contribution scheme cant, so if the public sector moved to defined contribution, then it would have to pay the COAP on top of the DC pension. I reckon that this could end up more expensive for the majority of public sector employee as due to their low salaries, they do not currently get any value for money for the 6.5% contribution they make as the COAP has eroded the % of the final pension that this pays for. From an acturial point of view, I reckon the government makes a profit out of these contributions in net present value terms.
You take a low paid public servant who received 50% of salary of 30k per annum = €15k. The COAP is 12k, so they pay 6.5% of their annual salary for 40 years i.e. 78k in total, in order to get only 3k net in return. They would need to live for 26 years post retirement for the government not to make a profit out of them. As life expectancy in this country is c.78 i.e. 12 years post retirement, the government is in profit out of these contributions.
If these contributions went into DC scheme, the Government would not make a profit out of the clerical staff pension scheme and would probably also have to match the contribution thus resulting in an even greater loss to the exchequer.