Inventor HSM turning operations attempt to remove all the remaining stock possible with the selected operation type. Using geometry Confinement, the toolpath can be contained within a specific region of the part.
Do the following to use geometry confinement:

The Frontside stock offset and Backside stock offset parameters can be used to extend the toolpath outside of the containment regions, or restrict the toolpath further within the region

No Frontside and Backside Offset

Positive Frontside and Backside Offset

Negative Frontside and Backside Offset