The choices in the Adobe PDF Preset menu are just presets of the options in the Compression panel, so if you want to “outperform the standard smaller size option,” you want to change the values in the Compression panel to be lower than they already are for Smallest File Size.
For example, for Color Bitmap images, Smallest File Size is set to 100 ppi for images above 150 ppi, so you can lower both. If all images in the document are already above 150 ppi then lowering the second value won’t make any difference, but all of the images will be downsampled to a lower resolution. Also, try changing Image Quality to Minimum. If you get a good result, save it as your own Adobe PDF Preset so you can choose it from the menu in the future.
However… except for the Compress Text and Line Art option at the bottom, the settings in the Compression panel apply only to images and not vector objects (paths). If there are no pixel-based images in the document, changing Compression settings probably makes no difference.
If the Illustrator document is mostly or all vector objects, then you can try lowering file size by reducing the number and complexity of objects. You can try things like deleting unneeded layers or artboards, deleting unwanted objects (such as choosing Select > Object > Stray Points and pressing Delete), and removing excess points from complex paths (such as choosing Object > Path > Simplify).