Newbie struggling with boundary conditions and meshing

[Mric237]

I've been learning openems for a few months and I'm having some problems with meshing and boundary conditions. For example, in the code below, I'm trying to reflect a signal off a ball and measure the signal with a discharge box above the source. I have previously placed two pec plates above the source so that I don't have to measure the signal earlier. So my questions are: firstly, how do I define my boundary conditions? Secondly, how can I adapt the meshing when I add the ball? Finally, how can I receive the reflected signal on my inbox, because at the moment, at the end of the plate, the sent signal diffracts and mixes with the reflected signal?
test_kugel_reflection.txt