I have this type bonnet guard with a slight raised lip on my Tucson and my younger brother has it on his car golf mk1 (rabbit shape).
We use to travel together for work and share cars and in both cars i noticed the drops flying off the guard striking the window about 1/3 up the windscreen at speeds of up to 70 kph. cant help but wonder how much of the air is actually deflected over the windscreen wipers. I then did a further test. A few days ago it was raining quite big rain drops but not a lot of them so i looked at how the patterns of drops flow off the windscreen while tailing a truck without switching the wipers on. When the truck turned off i noticed the drops moving a lot faster (predictable). i then sped up to about 65mph and noticed the drops in the bottom 1/3 to 1/4 of the windscreen not moving at all and the drops above streaking off to the top.