Date: 11 Teves 5576
From: Rabbi Moshe Sofer
To: Rabbi Yechezkel Segal
The question concerns whether text written between the lines (teliyah) invalidates Tefillin and Mezuzos, and the underlying dispute between the Sefer HaTerumah and the Ran about why. The Chasam Sofer permits suspension in Rabbeinu Tam's Tefillin, since their parshiyos arrangement already places text out of physical order, but declines to permit it for Rashi's Tefillin.
Source: Shu"t Chasam Sofer OC §8