the fume extractor over the welding bench at my former employment was HUGE !
the canopy covered the whole bench, and extended about 4" over the front and both sides.
the exhaust tubing was at least 8" or so, and when the fan was turned on, it really SUCKED ! [the FUMES that is. ]
this was before we got any mig welders, and after that, the fan was tamed down quite a bit so the suction didn't suck out the shielding gas. [we used straight CO2]
the drawback for not making the fan a two speed, was when stick welding heavy [thick] steel, the fumes took a lot longer to get sucked outside.
the vent was straight up through the roof, which was about 15ft or so.
this example might, or might not, apply to the OP. just an example of what i experienced at work for 42+ years.