To answer this question, we need to separate the Tier 1 ISP Peering Inclination from its articulated Peering Policy.
Definition: A Peering Inclination is a predisposition towards or against peering as demonstrated by Peering behavior in an Internet Peering Ecosystem.
Definition: A Peering Policy is an articulation of the Peering Inclination; it documents and defines the prerequisites to peering.
The Peering Policy is what one might find on an ISP web site, or it may be received after signing a nondisclosure agreement.
But to predict the peering behavior, the underlying Peering Inclination is important.