8 XXX : lingerie

Historically, garters were worn over any panties as it was more proper for a woman to be seen without stockings than it was without panties. Wearing garters under the panties is a more modern way to dress, due to the fetish of wearing stockings and no panties. Source: I am a costume designer that wrote a research paper in historical lingerie
I can imagine that wearing the panties over the garter would be a little uncomfortable in that the straps would more likely create tension at certain positions (like the one in the picture). Whereas having the garter over the panty would allow the straps to move freely.