With short lines where the text won't fit between the arrows, the text will move above or below, left or right, depending on what you select and in what order. NB: the following is assuming that your dimstyle Fit tab is like mine (see attached pic).
To get the text defaulting to the side you want it placed, the order you select the nodes is important. For horizontal lines, if you select left node, right node, the text will be on the right. To get it on the left, select right node, left node. If you are doing vertical lines, if you select the bottom node then top node, the text will be above. To get it below, select top node, bottom node.
If you are doing a single click to dimension the whole line, which half of the line you select is important.
Horizontal: If you select a point on the line left of centre, the dimension text will be on the right of the right leader line. Select a point to the right of centre, the text will be on the left.
Vertical: if you select a point on the line below the centre, the text will be above the top leader line. If you select a point above the centre, the text will be below the bottom leader line.
Hope this helps.