Ah, so you're using Force Displacement (or non-RTO) on these objects so that you can send them through the micro exporter? I wouldn't recommend that unless you have no other way to match their positions in Lightwave.
The random file sizes might be explained by duplication of polygons near bucket boundaries, but the numbers still don't seem quite what I would expect.
But if you are populating them, then all kinds of weird things can happen to very small polygons when using the rasteriser/non-RTO.
Matt