I finally figured it out. My initial bounding box was rectangular and wasn't centered at the entity's origin. I manually set the entity's bounding box like so:

wait(1); // wait 1 frame after creation
vec_set(my.min_x,vector(-7,-7,-20));
vec_set(my.max_x,vector(7,7,20));

And now I have perfect movement. I'll post my movement code in the tutorial area later today.

Thanks!!
- Bret