Child Start Date not matching Parent Start Date


Help! I am having trouble getting my child start date to match up to the parent start date.

I am using a "t-minus" type plan -- counting back from the project end date.

The future week's end date sets the start date of the week ahead. This is working great.

However, when I attempt to add duration and predecessors, everything gets wacky.

In plan below, Line 38 should begin on 5/18 with a duration of 10 days.

Line 39 should begin when line 38 ends with a duration of 15 days (I don't have the predecessor in now as it REALLY throws things off). The full duration of all tasks should be a total of 25 days.

How do I get line 38 to begin on 5/18??? The only way I can make it happen is put the full 25d duration in and it will work, but that does not get me the result I want as that duration is truly on 10 days.

Why is this happening?

I've added my project settings as well if that helps...