Query displayed on the y-axis of a dot plot

[mu-bio]

Hi Maria,
Thank you for this useful tool!

I have two questions.

1. How is the query displayed on y-axis of the dot plot selected?
   I inputed 20 contigs aligned to the reference genome, but the dot plot y-axis only showed 13 contigs.
   When multiple contigs are aligned in the same area, will the one with the highest alignment score be displayed?

2. What is the difference between "always" and "zoom" in the grid line option?

Thank you.