That code looks like it should work (just change 200 to 200.0 - Height is a double). I've just verified almost identical code on my machine.
Here's a few things you can try:
Ensure you're using the right name for the control - Select the control in Visual studio and check the name in the properties window. Lightswitch creates lots of name variations, and it's easy to miss that the actual name is "PersonList2" for example.
Ensure that you've selected "Pixels" for height control in the properties window for the control
Once you can access the Height property it won't actually do anything until you set the control alignment to "Top". If it remains on "Stretch" it will ignore anything written to the Height property.
Let me know if you still have trouble getting this to work.