I'll definitely be trying a different style blade.
Sounds like we have some contradicting ideas on pitch vs. vacuum. I was originally thinking like GMCL and the book. I don't follow his theory on the blade as an airplane wing changing vacuum due to the angle it's in. The angle of the blade creating lift is the cutting edge and rear lift wing of the blade not the angle it's rotating at. If you take a fan and lay it the floor it would blow up. If you tilt it at an angle it would blow at an angle. If you stand it up on it side it will blow side ways all due to the fan blades pitch not the angle it's rotating at. Now change the pitch of the blades by shorting them either direction or changing the angle they're bent at and this would change things. Angling it differently would only possibly increase or decrease the amount of air available to the suck side of the blades there by somewhat increasing or decreasing the flow. For example if you laid the fan on the floor blowing up the limited clearance between the fan and floor could cause a restriction/reduction of air available for the fan to pull in. On the other hand if you take a carpet vacuum and place the suction apparatus closer to the floor it has better lifting power. If you move the apparatus father away either straight up or tilting it you loose suction or lifting power but you may have more volume or air movement.