Using Rsoft's solar cell utility; should height of source matter?

We're using Rsoft's solar cell utility to simulate plasmonically enhanced solar cells. Being new to using Rsoft I was curious if the distance between the source and the top surface of the cell would effect the cell's Jsc and overall efficiency. I expected it shouldn't, but it turns out it did with my simulation file. I then opened one of Rsoft's tutorial files that came with the software, and ran a few simulations while only varying the height of the source. I found that the results were also effected by the height of the source. We tried emailing Rsoft's technical support, but received a very short answer basically stating the height of the source shouldn't matter. At this point, I do not know how much distance I should be putting between the source and the cell, or perhaps if the problem is arising from some parameter I am missing. We are currently running a similar simulation in Lumerical, and are hoping to get a better idea of where the source should be once we get the results back from that. Any help or suggestions would be greatly appreciated. Thanks!