You can specify the maximum distance away a Pokémon can be for notifying you.
Simply pass the distance (in meters) to the --range flag.
By default, the range is set to 500m, but can be increased to a maximum of 1,000m (1km).
Example:
pokevision watch \
--lat=40.712774 \
--lon=-74.013408 \
--name="World Trade Center" \
--range=100