Excess oil in fan grease trap after stir frying in a wok
Partial answer to the new formulation: 


  how do I make sure the oil goes into the food, not into the fan? 


You don't. The oil is not supposed to go into the food that's being fried, it should be fried at the temperature where it does not soak through, else it becomes quite unappetizing. It is normal that you get a lot of oily vapor when frying, especially at higher temperatures, you cannot prevent that. A splatter screen is sometimes used, but it is not suitable for wokking, because you can't move the foodd items with it. 

As for what is the right amount of oil, I can't help you exactly because I don't do much wokking on my own. But I suppose good temperature control will indeed use up more fat than modern Western cooks tend to use. 

There is a related question of a user complaining about oil splatter, and the conclusion is the same: you have to live with it. Good way to prevent grease build up in kitchen?.