CST Field Contours bad resolution?

Hi,
I'm simulating a simple microstrip structure (picture). I tried different mesh-settings to have a better field resolution (looking at the e-field which seem to be kind of square-cut) but nothing changes. S-Parameter are also almost constant for even finer mesh. Is it a purely grafical issue and if yes how can I solve it?

It is a graphical thing. See the mesh lines ? they match with the hexahedral mesh lines. If you have the frequency domain solver you can use it with fine triangular mesh around the edges if it is really important.