Origin of a Dimension is always Centered and cannot be moved.
This is caused by the Arrowhead Workflow, Automatic Orientation being toggled
ON. Toggling this OFF will allow placement of the dimension, or the origin
editing to be other than Centered.
Assure this is toggled OFF in the Template Part File in the Drafting
Preferences before creating a New Drawing.
Toggle this OFF in the existing Part File in the Drafting Preferences before
creating Dimensions.
For existing Dimensions, edit the Settings of each Dimension and toggle this
OFF.