I am able to communicate with the printer by Octoprint, or using the Smatto Motor tool by USB, or through Slic3r over USB. (not all at the same time of course).
I am trying to follow this guide - https://mattshub.com/2017/04/19/extruder-calibration/
Currently my setting are as follows;

When i try to extrude 100mm using G1 E100 F100 i get ~85mm extruded. This is pretty consistent.
I have tried making small adjustments to the Motor Step value, and i have tried doubling it and halving it - but nothing seems to make any difference.
Hot end temperature while trying to do this is set to 200c but i have tried changing it to 190 and 210 - after printing a temperature tower from Thingiverse this particular PLA seems to work best at 190c.
I'm a bit stuck at the moment because nothing is changing - so i assume i must be doing something wrong.
Thanks in advance for any help