When adding a Horizontal (or Vertical) Dimension to a drawing the last prompt is to Specify Dimension Line Location. There seems to be some minimum distance it must be from the object being dimensioned. Often it is much too far from the object. I can make it be even further away, but I can't get it any closer. I was trying to define three sections of a rectangle, but I couldn't get the middle section (dimension) lined up with the two outer sections. It wanted to be too far away. There was plenty of room and a very simple start of a drawing. Not a unique experience, I have had several of these. (ver 2.2.0 rc-3)
You can use snap-to-grid to place a dimension line at a prescribed location, Also, if you need to adjust the position of a dimension line, by selecting a dimension line you will see its handles - the dimension text / line / extension end points can be adjusted by dragging the handles.
If you have Free Snap on and other snaps off you can place the dimension line at any position.
You can change snap settings during an operation (as you need to have some snap on to specify extension lines origins).
Another, maybe more convenient way is to zoom in very closely when defining the position of the dimension line. This enables you to place the dimension line closer to the object without getting snapped to the endpoints.