making soy yogurt

i know there were some thread awhile back about culturing and yogurt making. the kids and i love yogurt. anyways, that thread encouraged me to buy a yogurt maker. i have tried to make two batches so far and never seems to get thick enough. the first time i thought maybe i didn't let it sit long enough about 10 hours. the second time i think it was 20 or so hours. i used silk soymilk and a culture.

does anyone has any experience making soy based yogurt? also, i noticed the wholesoy store bought yogurt has corn starch and tapioca starch add to it. should i add them to mine? any ideas, recipes????