You aren't using those lines, you are using the values linked to the blue portion.
I.e. You are trying to say, when candle crosses yellow line, exit trade. Yellow line doesn't exist in the code. Only visually. That is why you can find the "value" of the 2 yellows on top and bottom....because they happened to be the top and bottom of the only 2 buffers that are available. Those 2 buffers, blue and red.
I think if you can change your thought process in that regard, you may find a different way to find what you're looking for. However, I am new to all of this stuff, and I'm sure someone else can tell me that I'm wrong....but of course if you throw enough variables at something you can make anything happen. But I think if you understand it as I am explaining you will see that the method you are using may not work. I know i've seen a few threads here involving objects being problematic.