It appears you have the concept correct.
One point, CAESAR II places the full thrust load on either side of the XJ. This is an adequate model for the most part. Your concern here points out that it is not always good enough. But you may want to also consider the point where you apply F2. The surface on which most of the pressure occurs is the elbow in your illustration.
If I say that the pressure thrust is equal to pressure times the effective bellows area (Ftotal), I could say that Ftotal = F(pipeID)+F(differential); where F(differential) uses the difference in area between the bellows effective diameter and the pipe ID. In this case F(differential) would be applied at A and B and the F(pipeID) would be applied at the equipment anchor (a simple increase in your anchor load with no effect on the other results) and also applied at the elbow. [With an anchor on either side of your XJ, I see no reason to go to such detail here.
These pressure thrust forces are everywhere in your system but axial pipe stiffness makes them trivial - except here where the XJ, itself, may allow axial response.]
Also, when calculating and locating pressure thrust you would also find a pressure thrust surface at any ID change along the line.
And, if your F1 and F2 would always be used together, both loads could be identified as the same force set (e.g., F1).