What I think you should do is try not to run a perfect setup for when it is dry or wet. Run a setup that is in between the two. That way you will be more consistent. Even though the XB8 allows you to set a perfect setup much easier than other cars, you should rarely do this because as you have experienced, track conditions often change so what you want to focus on is a setup that works good in all areas rather than be perfect in any particular one.
That's because in offroad the conditions change a lot throughout the day and besides, different parts of the track will have a multitude of different conditions anyway.
If my car works too good in any particular area, I start looking for the weaknesses and dialing that strong point out because that is bound to mean that it won't work all that well in some opposite condition that is bound to occur.
Then once you get a good setup that you are comfortable with that works well just about anywhere for you then stick with it and work on your driving skills.
![Wink ;)](./images/smilies/icon_wink.gif)