When data is merged, objects can grow in both width and height from the anchor point. Because any expansion of the object occurs in the opposite direction from the anchor point, the anchor point may restrict the direction in which an object may grow. For example, if you choose an anchor point of Top Middle, the object may grow to the left, right, and down.
Caution:
The Expand To Fit option should not be selected for Acrobat 6-compatible forms. Users cannot edit the data in expandable fields in Acrobat 6 compatible forms. Instead, you should position and size fields to accommodate the longest possible user-entered data value.
See also

To make objects expand to fit