CST MS port extension coefficient

Hi,
I am new to this forum and also new with using CST microwave studio.
I have a question.
When calculating port extension coefficient, sometimes I got minimum and maximum value for K, why this happens ? is there something wrong with the design ? If not, which one I should select because there is deference between the results when simulating with min and max K.
Also other question
Can I use parameter swap for K and how?
Thanks in advance.

You can sweep K if you use variables for port construction. The simulation result dependence on k should be small for correct k - values. It also depends on mesh density, you should run your simulation with adaptive meshing.

You mean I should use wave guide port construction method enstad of Port calculator? Other thing... How to know the correct k value?