I would like to know the correct setting in Magmi needs to be set so that the magento "thumbnail" attribute is set to "small_image". So that all the products on my site will use the "small_image" for thumbnails.
For example, using the "Default Values setter" and setting the thumbnail attribute to "small_image".
Please help me.
Surely this has nothing to do with MAGMI, you would set the images using the Images Attribute processor;
http://sourceforge.net/apps/mediawiki/magmi/index.php?title=Image_attributes_processor
on import but to determine which one is used in the frontend you'd modify your theme's relevant template and pull the small_image rather than the thumbnail;
helper('catalog/image')->init($_product, 'small_image')->resize(135); ?>" width="135" height="135" alt="stripTags($this->getImageLabel($_product, 'small_image'), null, true) ?>" />
