The EU process is very much mimicking the Paris Agreement itself. They have their central objective, which is pushed by the different nations as what is seen as the fair contribution for the European Union. Then countries are invited to say and to argue why their contribution is going to be such-and-such. It's in this argument that countries set their basis for why they should have the target above the target or below the target. Then this is negotiated afterward, as a process.
Giving the countries themselves the voice to argue their case is very powerful in that respect.