Michaela (your name sound very German),
if you check the information about an airdam, be aware, that a lot of them looks aerodynamic, but they are not.
I have currently on a other (e-mail) list someone, who likes to do the same as you.
When I discussed his problems with the air dam, again I found out that the most of the comments and information he got about air dam, had nothing to do with the (correct) aerodynamic rules.
Sometimes a brick is more aerodynamic than a streamliner.......depense on the design....
If you like you can do the same what this guy done, contact me off list and we can discuss this special for your vehicle - not as a general view.
See ya