Vellattom is a minor version of the ritual enactment where the ornaments, decorations and parapharnelia are minimal thanks to which all actions including vaaythari (speech) is maximum and Attam (dance) will be at its peak. If you compare this level of enactment to the idol of a deity in a temple sanctum which is installed as per sathwic sasthra and vedic rituals, Vellattom is at par with the idol alone without the prabha-mandalam which circles it. A more easier example is the Seeveli ceremony with only the small idol on top of the elephant.