ASCE7 Spectrum Gen. R values from table 12?

Our client is looking for more clarification on the details of the spectrum generation built into the dynamic output processor.

The CII help for the R value in the spectrum generator says to use table 12 (value of 3.5). In ASCE, that table is for building modal analysis, not piping analysis. How is this value applied to generate the spectrum? The table in chapter 13 (Rp value is 12 for piping) is applied in a static method. Which is more conservative?

I can't seem to find any details in the technical reference manual on the R value for spectrum generation.

To clarify more, I'm running a dynamic analysis with an ASCE 7 spectrum. The issue seems to be the how the spectrum is being generated, specifically some confusion around the R value.

R appears in the denominator so 3.5 is more conservative. I believe B31E now specifies the use of 3.5.

Yeah, that part I understand. How is the 3.5 determined? Any literature reference? Why isn't it 2 or 4 or 6?

Thanks!