When you allign the white balls, are they sitting above where your foot is or are they where your knees at? Also i agree with mmd models as some are broken as high heels or something would make the model a pile of mush. Try use the public avatars first and see if it works as i had to use them to get a general idea of how to set up the white balls. A good one that works really well is the X and Y models. Greg uses these in his videos as they are the best ones to use for full body tracking unless you create one with simular height and bones.
EDIT: If you are having bending knees problem then goto the world called TUTORIAL (Vive or oculus) then calibrate your height through that world. You could also fiddle with adjusting the leg correction on the Driver4VR program in the calibration menu. (Make sure to press enter to apply changes)