How much subglottic extension from a primary glottic tumor would make you treat the regional lymph nodes?

This is a question that may be more complicated than it looks, though I recognize that Dr. @Dr. First Last has a wealth of experience in this area.

The first issue is that the definition of the cranial extent of the subglottic region is not standardized. It can vary from just under the cord to 5 mm ...

The top of the trachea.