Understanding XY resolution (no replies)

Hi, I have built and been running successfully a home designed reprap cartesian printer based on a Gen 7 main board with Marlin 1.1.x firmware. I have been looking to improve the resolution on my X and Y axis. My current steps /mm is as below:

#define DEFAULT_AXIS_STEPS_PER_UNIT { 11.94, 13.93, 500, 129.7 }

Taking my X axis for example this should translate to 1/11.94 = 0.083mm/step. In my host controller - which is Simplify 3D – I tried finding the smallest X movement I could get the printer to move. I assumed this would be 0.08 mm since that would be one single step of the motor. I moved the X axis to 100mm from the home position and then sent a G1X100.1 F1 (the F value was set as low as possible so I could roughly count the steps the motor moved. ) I found that I had to increase the move to 100.4mm before I got any movement of the motor and then the motor moved about 3 or 4 steps to go from 100mm to 100.4mm. Further increasing the move distance resulted in no movement until G1 X100.8 F1 and then the motor moved the same distance as before.
I don’t understand why the smallest distance I can resolve to is about 0.4mm. I would have expected 0.08mm. Is there some setting in marlin that is preventing the resolution from going below 0.4mm?