Partial neck sizing usually refers to pushing the case into the sizing die just far enough to size the neck most, but not all the way to the shoulder. The idea is to leave a little of the expanded neck from the last firing to help center the bullet in the chamber. The shoulder is not set back at all when you do this, as the shoulder never gets far enough forward in the die to touch it. If you set shoulders back in a standard die, the neck is being fully resized every time.
To get a partially resized neck plus shoulder setback, you have to size the neck part way first, then set the shoulder back in a separate body die that is too wide at the neck to resize it. Redding makes body dies. A full-length resizing bushing die with the neck bushing removed will also do this.