The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the global climate. In a context of global warming, modelling the AMOC is essential to analyse the long-term variability of the AMOC and its responses to historical forcing, which cannot be investigated by sparse observations. However, the simulated AMOC is not necessarily consistent across model resolutions. Here, we use a hierarchy of the global coupled model HadGEM3-GC3.1, at resolutions ranging from 1° to 1/12° for the ocean, to evaluate the sensitivity of dense water formation to horizontal resolution over the subpolar gyre. In line with observations, the models show that the mean overturning and buoyancy-induced transformation (WMT) are concentrated in the eastern subpolar gyre rather than in the Labrador Sea. However, the magnitude of the overturning at medium and high resolutions are significantly larger than in the observations. This disagreement is mainly attributed to large WMT over the subpolar gyre instead of anomalously large interior mixing or overflow transport from the Nordic Seas. Over the Labrador Sea, the intensification of WMT with resolution is mainly explained by two main processes: (1) on one side, anomalously warm surface water enhances turbulent cooling and reduces the extension of marginal sea ice, which further increases the density flux over the boundary of the Labrador basin; (2) on the other side, a bias in salinity leads to anomalously dense surface water that shifts the outcropping area of the MOC isopycnal from the interior to the boundary of the basin.