I have already installed (a relatively small) splitter in my car and am now considering the addition of an air dam
mods are made to reduce drag and not lift. but if I can lower both even better 
the problem is I cant seem to get "a right answer" when I search for the air dam's possible location
a lot of racers seem to favor the "air dam above and after" the splitter meaning the splitter extends below the air dam and in front of the car
the wrc car approach is an air dam in front of the splitter
and lastly , I recently saw a bluemotion golf notorious for its "extra aero features" and it seemed to have a small air dam below and after (!) a straight area -lets call it a splitter-
I am considering the "wrc approach" to be honest but a lot of guys that run track days say that
"to get max low pressure all you need is to speed up the flow. Trying to reduce airflow at the same time will have the effect of reducing the effectiveness of a splitter. Most likely it will cause turbulence under the car and increase pressure thereby creating lift"
or
"Placing it under the splitter will have a negative effect.
Will cause the airflow under the car to become turbulent and there for slow it down and create lift.
Yes The function of a splitter is to stop air from hitting the bumper and going under the car (therefore reducing the amount of air going under and more over pushing the car down)
But it also serves the purpose of creating a a flat surface which allows air to cleanly flow underneath which speeds the airflow up reducing lift.
Having the splitter protrude down will create a lip with a low pressure zone directly behind it causing turbulence"
after the air dam I am thinking some front and rear tire spats (I have taken photos again from the bluemotion golf, rather interesting) but that is another topic
what do you guys think? sorry for the long post and many photos but I tried to include everything to be specific