Maybe try putting baffels on either side of the hood to direct the bad air up towards the fan - This can , I believe be done with clear acyrylic panals so it wouldnt obstruct your visual space. My set up is just the 8" pipe coming down to about 12" up from my table top (no hood) My torch is pointed towards it , my cfm is 800 but I think it could be less, since there is so much pull,
Kinda like this: (right pic)
Ps I'm NO expert but this seems to be working for me.