In a high hp build or a bike which has to see sustained high speed, ( one customer was sitting on 200kph on the way to work for an hour each morning and night) I usually add some height to the tube where the little filter sits on. I have on occasion added a couple of little "S" bends to the tube so the breathing vapours hit the edges of the tube and the oil runs back down. FWIW the bike mentioned above, was operated at those speeds daily in 40+ degC and after a time I suggested he change from 15/50 oil to 15/60 , which he did and the problem stopped.