Yes, you need to adjust the e-steps in the firmware settings.

Not all extruders extrude the same length of filament for the same number of e-steps. If your slicer thinks that 615 steps will feed 1 mm of filament through the extruder, but in reality 200 steps are needed, then you are over-extruding by a factor of 619/200 = 3.095. You can adjust that by making the multiplier 1/3.095 = 0.32, but that is a kludge as the extrusion multiplier is intended to account for flow properties, not filament size issues. Better to adjust the e-steps in the firmware or you will have to adjust the multiplier for all filement types.

You can google the correct number of e-steps for the itty bitty and start from there (and reset the extrusion multiplier back to 0.9 for PLA in S3D).