Turn on Flat Area Detection, and it will go to it's proper depth. If you don't have that turned on, it's going to default to the Rough and Fine Stepdown increments

On another note, your method of selections on the 3D adaptive is not quite proper. Stock Contour is used to define where there is stock to account for, not so much (in this instance) where you want it to cut. For that purpose, you would want to select "Selection" and define the 2 areas to cut.

And one last note:
The Adaptive clearing operations are Roughing passes, not intended for finishing features. They will typically not leave a good finish, it will be faceted. On top of that, it uses the tolerances you set in the operation, and it might just violate the intended feature size if you leave it to go to finish sizes.
Seth Madore
Owner, Liberty Machine, Inc.
Good. Fast. Cheap. Pick two.