After a number of test bookings, it appears that a companion pass booking allows a maximum of two connections that exceed 4 hours for the entire itinerary. This seems to be regardless of whether or not they show up as valid, bookable routings with companion charges in the system.

A routing with SEA-PDX-ANC-OTZ outbound and BRW-ANC-LAX-PAE worked fine. On the outbound, each of the connections was < 4 hours. The return had two connections > 4 hours.

However, if the outbound is changed to SEA-ANC-OTZ with a 4 hour 8 minute connection, there are now 3 connections > 4 hours and it is not bookable with a companion pass.