The B31 Codes mandate very few things. And all of what we do is, ultimately, defined by Code requirements.

But common sense is much more demanding. CAESAR II is an APPROXIMATION to real-life behavior of piping system components. The authors of CAESAR II have had to choose between rigorous mathematical solutions to the governing equations relevant to piping systems, and approximations which enable faster and more stable solutions. (Many of the mathematically rigorous solutions to the governing equations may not converge reliably, and in many more cases, there simply is no mathematically rigorous solution.)

So, when those responsible for the software recommend that you follow a particular guideline for certain types of problems, it is simply not sensible to ignore their advice.