I say the reason soldering fumes/smoke drift your direction, is because your body heat causes an updraft of heat, which causes the vacuum, (Filled with fumes); of cold air, to be drawn up your nostrils. As you solder, the fumes/smoke.... jump in to fill that vacuum left behind from the heat leaving your body. Thus, smoke up your nose. Same reason that a shower curtain sucks in at the bottom. What saith ye? I know......how profound!