Sorry to keep you waiting, just got back in
Try:
<mapping ai_variable="wet_weather_ability" characteristic="wet_weather_ability" type="NEFloat" value="1.0" num_limits="4">
<limit difficulty="0.0" characteristic_value="0.0" />
0.90</limit>
<limit difficulty="0.0" characteristic_value="1.0" />
0.95</limit>
<limit difficulty="1.0" characteristic_value="0.0" />
0.90</limit>
<limit difficulty="1.0" characteristic_value="1.0" />
0.95</limit>
</mapping>
Don't ask me to explain as I did it by trial and error, but the .90 to .95 seems to be a range and the two pairs of lines relate to the ifficulty setting I believe. So I just put the same range in both pairs of lines, in this case, 0.90 to 0.95, but if they are still too fast, try 0.85 to 0.90 in both.
I am currently using 0.93/0.98 and can see a definite improvement, but I'm still tweaking it race by race; it is now MUCH better than before for me, hope you enjoy the difference