Object snaps become active when the object snap target box passes over an object
location such as an intersection or endpoint. Depending on the complexity of your
drawing, you can increase or decrease the area that is influenced by object snaps.

You can also change this setting in the Options dialog box, Drafting tab.

The APBOX system variable controls whether the object snap target box is displayed.

To change the object selection pickbox that is displayed at the Select Objects prompt,
use the PICKBOX system variable.

The following prompt is displayed.

Object snap target height

Sets the height of the object snap target box in pixels. The higher the number, the
larger the target box.