Yes, exactly.  Atharvan is never used in a way comparable to nirvāṇa or nirvṛti.  Atharvan is a person, or personification of the Atharvaṅgirasaḥ/Atharvaveda.  The head may indeed signify metaphorically the chief part or pinnacle of anything, of course.

Tim

From: David and Nancy Reigle <dnreigle@gmail.com>
Date: Monday, January 16, 2017 at 8:09 PM
To: Madhav Deshpande <mmdesh@umich.edu>
Cc: Tim Lubin <lubint@wlu.edu>, Indology <indology@list.indology.info>
Subject: Re: [INDOLOGY] textual source for nirvāṇa-mastaka

I understand the Vācaspatyam's definition of nirvāṇa-mastaka, nirvāṇam nirvṛtir mastakam iva yatra, as saying that this nirvāṇa is like the head. Whereas, in the second verse you quoted, Tim, the construal is atharvaṇaḥ śiro, the head of atharvan. But we cannot say for nirvāṇa-mastaka, the head of nirvāṇa. Is this the point?