If you scrutinize these pictures provided you will see that the walls are not fully painted to the top.
Why do you think the black pain was not painted until the whole walls and those ceiling beams are totally black.
The main purpose to pain you BH using those black coloured water based paint was to reduce the light reflection from one wall to the other.
Remember we need the nesting rooms to be as dark as you can.
My recommendation is to be as dark as possible until when you stand about 2 feet apart you cannot see the other person's face.
However you must not paint until the ceiling.
This is due to these swiftlet do need some light in the morning to find the entrance hole out.
If you paint every thing you will find that those birds will not want to start too far away from the entrance hole area.
Of course there are many other things that will cause those birds do not want to stay too far in.
If you BH is with a single entrance hole and this particular hole faces the west, the same thing will happen.
This is mainly due to the fact that the morning light tend to take a much longer minutes to get inside the nesting rooms.
Those birds will therefore prefer the area very closed to the bright areas.
You need to perhaps consider to open an additional hole facing the east. This additional hole can be as big as 1'X1' just enough to allow the morning light to shine inside.
With this arrangement I can safely says that your VIP rooms that are located further away from the entrance window will stand a better chance to have some nests.
The main lesson you learn from this article is that:
1) Never paint all the walls up to the ceiling.
2) Allow about 1 to 1.5 feet of the wall ceiling downward to be a brighter colour (white).
3) If your entrance hole is not facing the east, try to open a second entrance hole. A small window will do.