By increasing the layer height, you increased flow, thereby getting better extruder control which eliminated the flow dynamics problems you had.
However, with good flow dynamics control and daring to take more time, you can actually obtain much higher resolutions.
With my X1, I occasionally use 0.04mm layer height in adaptive layers to provide a bit of a margin to the just about still doable 0.02/0.03mm layer heights. Once flow went as low as 0.01mm³/s though, I reached my limits.