One challenge i find with large bore fittings - tees in particular - is that the quality control is low, and you'll want to talk to your manufacturer to see if you can get an appropriate minimum crotch radius for purpose of estimating SIFs and flexibilities.

There is a "normal" practice of using a crotch radius equal to 130% of the wall thickness.

Using a bigger crotch radius results in a stiffer tee with lower SIFs. Higher loads, but usually a higher capacity to absorb those loads.

Crotch radius is difficult to measure or control.

You can also opt to move to a thicker wall for your fitting itself. This is often preferred to trying to garner flexibility from the pipe itself, unless you possess a large amount of real estate and the expansion loops and whatnot are more cost effective (often no).