Sleeper Stub is used to define extended geometry that supports long sleepers on the branch.
It is defined in the turnout Feature Definition and it is used if you check the box Use Sleepers Stub when placing the turnout.
You can set:
If Entrance and Exit Radius are not the same then it does create a transition from one to the other.
If you are using radius, Fixed determines if you apply bending on radius or not.
Note: a defect has been identified in version 2020-R1 (10.08.00.88) when Fixed=True is applied. The radius is divided by 2.