*.ssa/*.ass size issue

[Simon_Haddad]

TL;DR: For some reason the background box of subtitles is always larger on the the right side than the left.

I am trying to write a script/program (for now a self-contained web page) that converts line 21 closed captions (for now in the form of McPoodle's closed caption disassembly format) to Advanced Substation Alpha format. The goal is for accurate simulation of the original closed captions, including timing, and with onscreen size and positions per the last page of the specification.

(repeating myself, sorry) For some reason the background box of the simulated captions is always larger on the the right side than the left, and always the same amount. It's not a deal-breaker and I might not have noticed if I hadn't developed a grid overlay that pointed it out to me. Can anybody guide me in the right direction?

Each line begins and ends with a non-breaking space to improve readability (as permitted in the second-to-last page of the spec). The font I’m using is monospaced and has the same character aspect ratio and same height-per-point size as Lucida Console, which carries the same distortion.

I'm including headers and relevant lines for the subtitles (and the code for the grids as a gift) in code boxes and attaching their relevant screenshots with grids below.

Thanks in advance for any help you can give me.

Here is the 4x3 header

[Script Info]
; Script generated by disassembly2ass
;
Title: omitted
ScriptType: v4.00+
PlayResX: 1440
PlayResY: 1080
Timer: 100.0
WrapStyle: 0
ScaledBorderAndShadow: yes
YCbCr Matrix: None

[V4+ Styles]
Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour, BackColour, Bold, Italic, Underline, StrikeOut, ScaleX, ScaleY, Spacing, Angle, BorderStyle, Outline, Shadow, Alignment, MarginL, MarginR, MarginV, Encoding
Style: Default,CCapbofira,53,&H00FFFFFF,&H000000FF,&H00000000,&H00000000,0,0,0,0,127,100,0,0,3,1,0,2,0,0,0,1

[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:12:47.37,0:12:51.17,Default,,0,0,0,,{\an1\pos(540,810)}\hand where is this\h
Dialogue: 0,0:12:47.37,0:12:51.17,Default,,0,0,0,,{\an1\pos(540,864)}\hBrisco County, Jr.\h
Dialogue: 0,0:12:47.37,0:12:51.17,Default,,0,0,0,,{\an1\pos(540,918)}\hof yours?\h

the 4x3 screenshot

[Attachment 83979 - Click to enlarge]

the 16x9 header

[Script Info]
; Script generated by disassembly2ass
;
Title: Accurate Simulated Closed Captions
ScriptType: v4.00+
PlayResX: 1920
PlayResY: 1080
Timer: 100.0
WrapStyle: 0
ScaledBorderAndShadow: yes
YCbCr Matrix: None

[V4+ Styles]
Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour, BackColour, Bold, Italic, Underline, StrikeOut, ScaleX, ScaleY, Spacing, Angle, BorderStyle, Outline, Shadow, Alignment, MarginL, MarginR, MarginV, Encoding
Style: Default,CCapbofira,53,&H00FFFFFF,&H000000FF,&H00000000,&H00000000,0,0,0,0,131.5,100,0,0,3,0.5,0,2,0,0,0,1

[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:08:59.37,0:09:01.94,Default,,0,0,0,,{\an1\pos(372,810)}\h-so, you know, here we are.\h
Dialogue: 0,0:08:59.37,0:09:01.94,Default,,0,0,0,,{\an1\pos(540,864)}\h(chuckles)\h
Dialogue: 0,0:08:59.37,0:09:01.94,Default,,0,0,0,,{\an1\pos(414,918)}\h-(chuckles) I get that.\h

and 16x9 screenshot

[Attachment 83980 - Click to enlarge]