.ssa/.ass:

How to change the positioning of one subtitle just by a few pixels compared to the style it uses?

I am trying to use {\pos(x,y)}

The manual says that \pos tag uses script resolution coordinate system.

Two issues:
judging from my experiments, looks like the origin of this script resolution coordinate system is way outside of the top left corner of my video
x,y don't seem to represent pixels if I change x by 160, the subtitle moves by 473 actual pixels; if I change y by 160, the subtitle moves by 227 actual pixels

I need:
to set the origin of the coordinate system to where subtitles appear by default as defined in their style (or, at least, the top left or bottom left corner of my video)
x,y to represent actual pixels

In other words, to nudge subtitle by x=4 and y=5, I want to be able to do {\pos(4,5)}

Can I enable this by editing .ass text?