As Bryan pointed out more explicitly, and I noted by saying "as long as the settings are within the operation range of your servo", if you set the low number too low, or the high number too high, it will try to make the servo go beyond it's operational range and it can do all kinds of crazy things like, jam, vibrate, even melt! I don't know what the exact limits are on the servo off hand, but somewhere in the middle of the range is the best way to go.
So take my advice if you want this to go easy...
Separate the body of the damper from the barrel
Set your HM to run 800 - 2400 with Inverted output.
Make your HM go to 100% blower/servo output
NOW mate the body and barrel so the moon shaped openings sit directly on top of each other.
Then make the HM go to 0%, it should close completely. Then make the HM go back to 100%, it should open completely. If you are not getting complete open/close tweak your numbers SLIGHTLY until you do. The easiest way to tweak the settings is put your HM into the position that is not proper, then alter the number in the Config little by little until it is proper. When you save the config you should see the servo move just a little, if it doesn't move then you probably altered the wrong number.