I've had to remove youngsters from nest boxes and place them on roosts. They eventually learn.... Yes, they pººp a lot!here is the picture
3 roosts R
3 nesting boxes NB
3 stepping perches in front of nesting boxes S - one (S) is hidden from the view by the Roost
2 chicks seen hanging out on the edge of the nesting box during day time (luckily with their tails out)
View attachment 2411229
The only way I can see of expanding your roost space would be to put a few roosts perpendicular to what you have. Do you have any old branches lying around? That would save you from having to buy more lumber.