How does the P1 translation column horizontal shift (and other fields) work?

I really like Inkscape and I enjoy doing things in it, but even after using it for a while I have to say that many functions are obscure and counter intuitive (like the gradient editor).

My current problem is following: I'm trying to tile vertical line several times next to itself equidistantly. Like this, but all spaces equal:

So I tried to create Tiled clones. After several google searched I finally (manually) discovered that this function is located in Edit -> Clone -> Create Tiled Clones.

Then I started to meddle with the function itself.

On the image you can see that even though I configured 200% horizontal spaces for every column (and the result should have 3 columns) the lines are all on one place. If I set n% vertical shift for every column, the result is following (it works):

I guess I misunderstood the GUI tooltips and field names. Could you explain what each settings on this tab means and how should I use them all to produce desired result?

Please do not omit the full explanation for other visitors.