On the other hand you may not want to drop every frame to the floor as there maybe a jump that would get flatten out. Another way to do what you want (assumes the distance above the floor is constant) is to make a new layer that covers the length of the BVH and make the layer an ADD instead of Replace and on the new layer on the First frame only adjust the Y Translate for the BODY of the figure. Also make the layer a Constant type. What this does is move the BODY which is the Origin for all movements and brings it down. If the BVH then has a Jump it will move up like it is suppose to.

Poser 5, 6, 7, 8, Poser Pro 9 (2012), 10 (2014), 11, 12, 13