Sorry,
It seems that each bar of lines has one active kill spot, which is a pixel thin. When both sides kill you, it would mean that there is a double layer of the red bar, each with a kill spot on the opposite side.
That said, you can abuse this in areas where you weren't supposed to be on one side of the line. In the above images, I simply walked or bounced in, originating from the warp-secret that leads to the mysterious red forest. It is also possible to enter the inside of a line with the green power-up if you to so from the end of it. If this wasn't clear enough, I can get screenshots of specific areas.