ASS subtitle - Different alignment at block and inner level
If you're familiar with an ass file, you can position your text by using \pos(150,250).
Example:
Dialogue: 0,0:01:00.00,0:01:15.00,Default,,0,0,0,,{\fad(500,500)\pos(150,250)}{\i1}{\b1}Your Text

The first number is from the left, and the second one is from the top of the video.
An easier solution, rather than write each line yourself, is to download Aegisub to make the ass files for you.
Using Aegisub, you can drag the text lines to the position you need.