Wow. Thanks for the quick responses.
I have messed with it and it looks like the lights can go high enough so that each light shines down on the tank at about an 80 degree angle. Which provides pretty good coverage from above. It still has to go through the plexi top which was my main question (does plexi inhibit any vital spectrum).
What about those lights? They seem like such a bargan compared to other compact fluorescent setups.