Your argument may be sound but I once again must say your rules (or better, the Code's rules for fully-restrained lines) conflict with the structural response of a collection of beam elements under load.

The rule addresses Poisson shrinkage, CAESAR II does not.

The Bourdon effect, in CAESAR II, will either extend straight pipe (option 1) or extend straight pipe and open bends (option 2). I might offer that a fully-restrained line has no response to that Bourdon effect.

I have no easy answer for your approving authority. CAESAR II is a good engineering tool. You and your authority can exercise engineering judgement.