If you're manufacturing the connection by cutting 2 pipes and welding them together, then PRG software is likely telling you an accurate story.

However, I'll note that I wouldn't ordinarily recommend installing piping in this configuration, but to use a forged fitting, which looks substantially different.

Allegedly, those forged fittings's flexibilities and stiffnesses are comparable to that of a regular welding tee.

Edit to add: The PIP standard has some short discussion on the topic, though it's roughly as verbose as I am above.