Hi,
you can also modify the properties of the PML layers to reduce further the reflections. To do this, go to Simulation-> simulate 3D (or 2D) and click the Advanced button.
You can increase the number of PML layers to further increase the overall absorption of the boundary (the maximum number is 100). Be aware that the more layers, the longer the simulation and the more memory needed. More layers will also increase reflections from glazing angles in some cases.
For really small structures and/or metallic structures, you can also increase the tensor parameter to around 80-85. Use at your own risk since it can also increase reflections in some cases!
Details are available in the documentation (technical background manual).
Aurelien