You can change the environment variable for your processing tool.

For a "one shot", click oon the environment > processing extent > union of inputs (or specify your own extent)

If you want this choice to be remembered, go to the menu > geoprocessing > Environment settings.

In Python, you can set the environment using arcpy.env

You can change the environment settings for your processing tool.

For a "one shot", click oon the environment > processing extent > union of inputs (or specify your own extent)

If you want this choice to be remembered, go to the menu > geoprocessing > Environment settings.

In Python, you can set the environment using arcpy.env