Krzysztof,
What you mean you added null point which follow lower rail. if your lower rail is changing from left to right that means that your null point also changing location ?? I am very interested in this,
By the way. There is another thing which I found. Cells is rotated with the base point at alignment. If your cant is rotated about inside rail (which is in Poland) and then you will place cell with i.e. sleeper and rails location is not proper cause of different rotation base point. so in your case when you have sleepers in template it will not cover where track is with cant.
So I suppose in this case we should create two cells with origins at left and right rail and place this cell separately for each curve ?? If it's true it's not a good solution.
Have you got any other idea??
Regards