Self-shading Question

I've had some confusion in the past about using the self-shading calculator in SAM. I think I've figured it out, and I wondered if you can confirm for me that I'm understanding it correctly.
Let:
N = total number of modules
S = number of modules along side of row
B = number of modules along bottom of row
Unless (S x B) is an integer factor of N, I'll get an error that says "The self-shading configuration for subarray 1 does not match the number of modules specified on the System Design page. Please check your inputs."
My understanding is that SAM is taking there to be [ N/(S x B)] rows of modules, with the spacing between rows determined by the GCR I choose in the system design page. Is this correct? If not, would you mind clarifying for me the points that I've misunderstood?
Yes, that is correct. SAM also makes other assumptions about the array layout and module constrution that are described in detail in the Shading topic in the Help system.