Again,
it's not the chemistry (synthetic vs. conventional) but viscosity and NOACK. If the oil consumption happens through the rings, higher viscosity probably increases the consumption. If the oil consumption happens through the valve-stem oil seals, lower viscosity increases the consumption.
"It must be recognized that viscosity governs in large part complex oil transport mechanisms to the upper regions of the piston - ring - liner system and therefore affects oil consumption. The low-shear viscosity affects different oil-transport mechanisms in different regions on the piston surface such as inertia forces due to piston movement, gas-flow dragging, and the interactions between the rings and grooves. The HTHS (High-Temperature, High-Shear) viscosity is believed to influence ring and piston liner lubrication and thus governs the oil transport on the liner."
In fact, this paper looked at the consumption of synthetic vs. conventional oil, and they concluded that the only factors that contribute to the consumption are low-shear viscosity (KV @ operating temperature), HTHSV, and NOACK. Conventional vs. synthetic otherwise makes no difference.
The contribution of different oil-consumption sources (PDF link)*
*The contribution of different oil-consumption sources to total oil consumption in a spark-ignition engine
Ertan Yilmaz, Tian Tian, Victor W. Wong, and John B. Heywood
Sloan Automotive Laboratory, Massachusetts Institute of Technology