The European Commission crucially relies on expertise and advice to fulfil its focal role in drafting policies. For this reason, it maintains numerous expert groups. When handling technical complex cases, expert groups engage in deliberative supranationalist problem-solving that is driven by logic and knowledge. Based on the Commission's policy initiative to develop European Public Sector Accounting Standards (EPSAS) for the integration of European Union member states' government accounting practices, this study investigates how and under what conditions policy incentives translate via expert group deliberations into draft policies. Drawing on policy design literature and using process tracing, this study finds that pre-existing policy instruments or design choices on higher order policy elements could lead to challenges in achieving the integrity and superiority of solutions at the level of calibration and street-level requirements, thus failing to produce the necessary expert consensus.