You can use the input box(es) to change the deformer’s dimension(s).
Different modes for deformation.
There are three modes for bend deformation.
The entire object is affected. Surfaces at a height between the top and bottom of the (non-deformed) cyan box are bent and the other surfaces are translated if necessary to accommodate the bend.
Surfaces within the (non-deformed) cyan box are bent. Surfaces outside the box remain exactly where they are (they are unaffected).
The entire object is bent.
Defines the strength of deformation. To change this value interactively, drag the orange handle in the viewport.
Defines the direction of deformation. 0° is the deformer’s local X axis. To change this angle interactively, drag the orange handle in the viewport.
If this option is enabled, the object keeps its original length.
This might be the best thing since sliced bread. A simple click on this button will adjust the size of the Deformer object to the Parent object to be deformed (i.e. to its bounding box). The object will be enclosed entirely and deformed as a whole. This means that the Deformer’s size must no longer be tediously adjusted manually (click here for additional information).
Furthermore, Deformer objects’ axes will be fitted to the axes of the nearest Parent object, i.e., you rotate the Deformer object interactively in the direction in which its effect should be exerted, click on the Fit to Parent button and the Deformer object will snap to the nearest axis (it will simultaneously assume this as its origin).
For some Deformer objects (e.g., Squash & Stretch), only the origin or other useful parameters will be fitted to the Parent object, depending on the function selected.