I figured it out Kevets...
A couple of things make it seem wonky.
I believe that because subtitling is essentially positioning text characters on a layer above film, your last character of the top line of text becomes your positioning element/point of reference if you're aligning RIGHT.
If you're aligning LEFT, then your first character of the top text becomes your positioning element/point of reference.
For example (RIGHT alignment):
T = Top Subtitle Line, B = Bottom Subtitle Line
T: Mr Smith
B: Walkin' along
...the 'h' and 'g' are justified, near the centre of the screen. If you lengthen the TOP line by adding more text, the more to the RIGHT goes the BOTTOM line.
You can fool the subtitler to flush your text more to the right by having a blank TOP line full of space characters and write your main text on a separate second line.
If you don't see any text, you've added too many spaces.
For LEFT alignment, think the reverse.
Hope this helps.