Wills, a couple other thoughts. Since the roots are concentrated on the bottom and are used to being in moist conditions it make make sense to water from the bottom, at least for a while. Alternatively, your suggestion about watering from the top prior to transplantation could actually be a good practice. Perhaps a couple of weeks prior to transplantation you could help prepare the roots for their new environment by letting the lower reservior dry up (or nearly dry up) and only water from the top.