Infuse 5.0.1 on iOS and tvOS does not show ASS subtitles with a \pos(x, y) command. Or rather, it seems to understand the command (otherwise the subtitles would appear at the bottom?), but all positional subtitles are stacked in the top left corner of the screen.
Example as seen in the attachment:
Dialogue: 0,0:00:00.00,0:00:00.89,*Default,NTP,0000,0000,0000,{\an8\pos(193.881,58.582)}{\fn汉仪双线体简\fs22\fscx120\b1\bord0\shad0\c&H2510A3&}前情提要
Dialogue: 0,0:00:00.00,0:00:00.89,*Default,NTP,0000,0000,0000,{\an8\pos(193.881,58.582)}{\fn汉仪双线体简\fs22\fscx120\b1\bord0\shad0\c&H2510A3&}前情提要
Dialogue: 0,0:00:00.00,0:00:00.89,*Default,NTP,0000,0000,0000,{\an8\pos(192.613,3.273)}{\fn汉仪双线体简\fs45\b1\bord0\shad0\c&H2510A3&}黑客军团
Dialogue: 0,0:00:00.00,0:00:00.89,*Default,NTP,0000,0000,0000,{\an8\pos(192.613,3.273)}{\fn汉仪双线体简\fs45\b1\bord0\shad0\c&H2510A3&}黑客军团
Also, these subtitles are bilingual, but around 50% of the time, the English half is missing. Example line:
Dialogue: 0,0:09:36.40,0:09:37.42,*Default,NTP,0000,0000,0000,我想过\N{\fn微软雅黑\fs14}I did.
All the non-positional dialogue lines use the same format and the same fonts.
(Of course, I wouldn’t even need to use bilingual ASS subtitles if Infuse could show two subtitle files at the same time ;)…)