First let me note that the current release of CAESAR II employs B31.3 - 2008 and 2008 rules in Appx. P are a little different.
CAESAR II defaults to equation (1b). If you want to see the more conservative allowable expansion stress range (1a), you must set that request in the Config file or special execution file. And, if you wish to use (1a), then I am uncertain of your interest in Appx. P as the intent of Appx. P is to avoid referencing the sustained stress in the expansion limit. You are already avoiding that reference by using (1a).
2008 code uses f in both the operating stress check and the operating stress range check. For A106 B, you can set f=1.2 (using the radio button in the allowable stress definition); that should line everything up for you.