Since Magento version 1.8 and newer it is not possible to easily export Base Image because it is not possible to add this attribute to Flat Catalog which is required by Koongo Connector.
Koongo Connector 22.214.171.124 and older
From the above mentioned reason Small Image attribute is set up as default attribute for image export in Attribute Mapping Table.
If you want to export Base Image you need to add following code to any config.xml file available at any module pool:
Subsequently, refresh cache and reindex all indexes. See further information here:
Koongo Connector 126.96.36.199 and newer
In connector version 188.8.131.52 the above mentioned code was impletented right into connector's config.xml so no further code tweaking is required for Base Image export. Specifically, the XML modification is executed only when the connector is installed in Magento 1.8 and newer. For Magento 1.7 the modification is not needed.