You'd still wait in the middle to turn right, even at a small crossroads (if you are the first one there.) A waiting place is not always marked. You only have to wait back behind the line if there is a green arrow for ahead or left, and a red light for turning right. If you are the second or third car there, you should only wait in the middle if there is space for your car. Some small crossroads only have enough room for one car to wait in the middle; but that one car really must move to the middle when they have a green!
It might be that you have to wait in the middle for a solid stream of oncoming traffic, with no gap until the lights change again, perhaps 20 or 30 cars. This is normal.
If the lights then turn to amber while you are in the middle (you may or may not see the lights then), you may still turn. When your lights go amber, so do the ones facing the oncoming traffic, so they will have to stop. So you should go as soon as you see the oncoming traffic slowing down to stop.
(Not wanting to scare you, but very very occasionally it can happen that a car gets stuck in the middle; they are still there after the lights have changed, and the other road now has a green light. This can happen if:
- Some of the traffic coming towards you disobeys their red light.
- Pedestrians cross the road you intend to turn into; you of course have to give way to them, as you are turning.
- You are too slow to move off from the middle after the lights have changed to amber, and the oncoming traffic has stopped.
It is very rare to get stuck like that; if it happens, keep the car ready to move, and go as soon as you can. Be careful if you have to cross more than one lane of traffic.)