I have never been convinced about down draft tables because inevitably some of the available air flow get blocked by placing the object being sanded on the table and light fine micron dust floats and never gets pulled down by the draft. The least I would do is put a three sided enclosure around the table to trap some of the floaters. Getting really pedantic about the whole thing a clear three sided enclosure and a strip curtain front like you see in some door ways would contain most if not all of the sanding dust. Over kill? possibly but it would fix the problem for sanding small stuff. We built a dedicated sanding room for a chair manufacturer which was ventilated by a CV Max and it worked brilliantly but not everyone has the space or need to go to that extent. The incoming air was dragged from the floor up and there was very little that escaped the air flow.
Chris
Everything I like is either illegal, immoral or fattening