Will close adjacent parts reflow?
Anything inside the visible IR beam will reach reflow. If the adjacent components are heat sensitive, you can mask them off with some reflective tape. As you have the visible heating spot you can work out which components you need to protect if need be.
If the adjacent parts are not heat sensitive then you do not need to worry too much as there is no airflow on our systems which means that the components will not blow about if they have reached reflow.