When the controversy raged about whether Hypo is heavier than water - (thus requiring bottom draining baffles) or whether it floated up - (your way of thinking) some test were done. The conclusion was that as it leached from the paper and the emulsion, it went into solution with the wash water. The most dominant factor was the flow of the wash water. Yes, technically it is heavier than water but not enough to overcome the influence of water flow.
Neal referred to the fill and dump method. This was shown to be the most effective. In this system, the washer is filled, allowed to stand for a short time and then purged. There were some isolated reports of print damage with this method but I have no firsthand experience with these systems
The most important factors were:
Space and separation between prints (since prints are often added as they are developed.)
Good flow across the surfaces of the prints
Time in the water to ensure the water had a chance to leach the chemicals out of the paper and the emulsion.
To test your water flow, try food coloring (Obviously NOT while washing actual prints!!) You will see if there is any pooling in the corners.