Turning the 2x4 the other way may help, the wide side parallel to the ground rather than up and down. All my roosts are that way. They can balance easier and rest their bodies on their feet to keep them warm in the winter. Since they are 5 months old and reaching their adult size, the...
Have they ever roosted on the roost?
The roost looks pretty close to the wall, so it may not be a comfortable distance for them. If their tails or heads are up against the wall they won't like it. Also, that jump is a lot. A ramp or something that steps up would be easier for them, even...