I'm assuming you're having trouble making shadows meet the character's feet? I don't know if your background props contain a floor - if not, use a prop plane, don't use the Poser ground. It has 'issues'. :) Drop to Floor doesn't always work accurately - Vicki 3 seems to suffer from this especially, for me anyway. But what's more important is that your characters' feet meet the ground, wherever it is - it isn't necessary for it to be at Y=0. I usually use one or more of the orthogonal cameras (front, side, back) and adjust the last bit manually.