The stages of deep ocean circulation during the Miocene remain uncertain, but palaeogeographic changes likely played a role in its evolution to the Atlantic-dominated overturning state of today. Regarding orographic changes, the uplift of the Tibetan Plateau is thought to be conducive to a shift from Pacific to Atlantic deep water formation, with flattening of the Rocky Mountains having the opposite effect. Here, we perform a suite of fully coupled climate model simulations using the Community Earth System Model version 1.2 (CESM1.2) with middle Miocene palaeogeography to assess the impact of orographic and CO<sub>2</sub> forcing on the meridional overturning circulation (MOC). The control simulation exhibits a strong Pacific MOC (PMOC; ~20 Sv) and no Atlantic MOC (AMOC). Flattening or widening the Tibetan Plateau has no significant effect on either basin's overturning. Flattening the Rocky Mountains strengthens the PMOC by 4 Sv by altering freshwater routing into the Arctic, but does not affect AMOC. A lower CO<sub>2</sub> simulation (2x PI CO<sub>2</sub>) yields no qualitative change in overturning structure, indicating that the PMOC is not solely a consequence of warm climate forcing. Our results suggest that Miocene orography influenced Pacific deep water formation but was insufficient to trigger a shift toward modern-like AMOC conditions. This implies that other tectonic and ocean gateway changes were likely necessary to enable the development of the modern Atlantic-dominated overturning regime.