Jonathan, my system is industrial my lines start are approx 3ft dia from motor to shop ceiling and reduce from there as they feed there dedicated line. My system cannot reduce to extract from portable tools for example.

To be efficient you must start with your lines large enough to meet the needs of the overall capacity of the line and natural drop in the draw as the length increases from the motor. I get a designer in its that simple, to get the flow correct as each auto damper opens and shuts and gets its full draw to meet the need of the machine it feeds. My spindle/CNC Morticer/bandsaw are not fitted with auto dampers and make up the 10% needed to work all the time due to implosion of ductwork if all system stopped drawing. My hand sander tables are fed from the extraction system and the power tools fitted to their own vacumns just like some of my chopsaws in assembly due to my extraction not being able to cope with portables.

MDF dust leak in my Beamsaw and Router is kept to minimum accordingly due to it being designed to operate efficiently. Extraction cannot be 100% due to saw draft or dust spitting out machined opening but you try to keep it down with ceiling intakes clearing the atmosphere and removing any fine dust. Some CNC Router now have a catch belt below the cutting table to catch spit/dropping residue from cutter and the belt conveyors it to a waiting pickup pipe at end of machine. The saw draft residue on my Resaw for example drops to floor or sits on machine table for vacumning. I do not have dust problems with my Optimiser saw as it it is in its own cabinet. I do have a Crosscut and have tried a few combinations to try catch the saw draft, but as it extends to do wider cuts is the problem and the suction drops from the catch can at the rear of saw.

I test my air/extraction every 14 months max for COSHH and legaility of UK H&S requirements. The personel dust monitors on workshop staff has proven itself to keep the dust air born to well near as enough not detectable. I have visited and worked in other shops where dust could be waist deep and the air thick with pollution. Cutting some woods you can be coughing or eyes watering especially with some of the hardwoods, you cannot do that in a factory not if you do not want litigation, plus it just looks poor.