Maws lists sfiii with 384x224. I don't have an arcade monitor, though, plus the more modern games are more likely to switch resolutions than older ones. (Not sure if sfiii is one of them that did.) And since MAWS can list only one res... the number listed might be one of the resolutions used.
i have read somewhere (correct me if i am wrong) that capcom designed the game on the "widescreen" proportions, because of memory limitations or something. but that the original arcade hardware would scale it to fill full-screen, like mame does without the ini file.
A little simplified but close enough. I'd say it another way: the confusion is that many PC users assume that pixels are square, when often they aren't, especially outside the PC world.
Square pixels is a PC computer thing (that HDTV also adopted). The analog TV signal (PAL or NTSC) does not have square pixels, and almost all arcade games did not use square pixels. CRTs (arcade or PC) do fine displaying square and non-square pixels, while PC LCDs have fixed square pixels.
If the pixel is 2:1, and the image designed for that pixel is 100x100, the image should be viewed at 2:1. For arcade games that display on a 4:3 monitor
(all of them), with a 384x244
sfiii image, the pixels are 7:9 (taller than wide). Arcade CRTs can do multiple resolutions, mame scales to simulate the different resolutions on fixed res
(LCD) monitors.
The thing is the OP has a real arcade monitor, so it can do the "scaling" itself instead of mame faking it.