I tried that, and on a single line with two trains it doesn’t work. The line got assigned to the left-hand platform and the first train entered it and stopped. The second train crossed the junction, also headed for the left-hand platform and stopped at the signal.
There’s no way to get it to the right-hand platform if both trains are assigned to the same line – you have to create a second line which will then assign to the free platform just fine.