MobileSheets will calculate the desired output path for the file (which depends on your selections under Settings->Storage) and it will just check to see if a file exists at the destination that has the same name as the file being imported. I normally recommend disabling "Create Subdirectory per Song" and leaving "Let MobileSheets Manage my Files" enabled on Android. In that case, MobileSheets will copy any imported file into the root folder of the storage location.
Mike
Mike