I remember CO had an ANC-SEA-EWR red-eye flight. SEA-EWR was the red-eye portion. In fact, I flew on the very last one, which IIRC was post-merge.

When based off of the Premium Cabin, UA doesn't use flat bed seating based on flight length, they use it based off of potential revenue. Using flatbeds on AK flights doesn't generate the premium revenue that the same plane would produce elsewhere.
When based off of Coach, UA doesn't use a wide body based off distance, it uses it based on the number of seats sold without over saturating the market.

Occasionally, widebodys are used on routes that are too far for a narrow body to travel without the need to refuel, but even then, if the yields are too low, they'll just axe the route.