I suggest that Velleman correct the extruder steps/mm in the controller firmware. The value is set to 600 steps/mm, which is wrong. It is very easy to measure the extrusion rate and discover that it is closer to 700 steps/mm.
Of course, a correct extrusion rate requires all the other parameters to be correct also. For example, the widths under the print settings “advanced” tab are incorrect because they were “fudged” to account for the incorrect extrusion rate.
Using correct parameters allows the K8200 to behave in predictable ways when parameters are “tweaked” in accordance with the existing literature - both books and Internet wisdom generally accepted by the community.
I suggest that it is time for Velleman to issue an update to the Repetier Host that has a more sensible set of default parameters. Of course, this will require instructing K8200 owners to measure the extrusion rate of their printers, and reflash the EEPROM (or change the value for E steps through the LED panel).
Regards,
Art Cominio