If you own a BH and your BH is new (less that 2-3 years old) you will observed that most of your nests will be at those corners.
If you installed corner covers the nests will be either on the corner covers or half on the plank and half on the corner covers.
A very strange thing and it will take another few years before you can get them to start using those straight planks.
This will only occur once all the corners were tenanted or taken up.
The new comers or babies bred from your BH will slowly occupy the nesting planks bit by bit.
Those who are not prepared or lazy to build their nests on the straight patch will in fact find a new house with lots of those corners.
So how can you attract them to build their nests on the straight planks?
My simple answer is to mobilize those fake nests that can be easily removed once it served its purposes. You might consider to apply those super pheromone on these fake nests to make them more attractive.
Yes once the fake nests were used and those baby birds flew away you can relocate these fake nests and leave the real nest on it at the old location.
I tried this before and I think it works.
Have a good look at the above nest being recycled.
You might want to watch this clip how I removed the silicone fake nest inside one of the BH that I managed.
After the removal I left the old nest without destroying it .
Before carrying this fake nest removal I make sure that there were no egg(s) of baby birds inside.
For this particular nest the fake nest broke and I could not relocate it.
If you choose the aluminium fake nest it will be much easier.
Have a look at these aluminium fake nests with real nest on them.
It will mush easier to remove or relocate the aluminum part and leave the nest on the straight plank.