What does it means "controlled" when we generate emulsion drops?

The injection method used in microfluidic devices, 3D glass-based devices and/or 2D soft lithography ones, affects the generated emulsion drops in their size and frequency formation. Our initial experiments in glass-based devices showed that under the same experimental conditions, the drops generated using syringe pumps were always larger than those generated using a pressure-driven injection. Further experiments in our lab have contradicted these results showing that how the experiments are performed is also a key element: if the experiments are performed with fixed outer pressure/flow rate, the drop sizes are always bigger when a syringe pump is used; if the experiments are done at fixed inner pressure/flow rate, that is not the case anymore. We argue that the stresses in the interface between the two liquids are propagated differently depending on which liquid is being the driver leading to different conditions to the formation of the drops.