Calibre inconsistently identifies device and sd card

Hi,

On my old Iriver Story Hd, Calibre sometimes identifies the sd card as "main," and sometimes as "card a." So to export to the sd card, I have to check how it identifies the sd card this time.

Also, despite the same instructions for folder structure, it exports files to different folders depending whether it identifies the sd card as "main" (SD Card > Book > Book > Calibre General > #genre > series) or "card a" (SD Card > Book > Calibre General > #genre > series).

Short of checking how Calibre lists the existing books, and ejecting and reconnecting until Calibre recognizes the sd card as card a, is there a workaround for devices with extra sd cards?

Thanks!