MaxSonar detection issue

For my current project, I'm using a XL-MaxSonar-EZ4 MB1240 (see next post) to gather range measurements, that I send to my PC with a Duemilanove. My problem, is that the sensor seems to be sending its pulses out at an odd angle. I found that in order to get an accurate reading from the sensor to a target of known distance (with good reflectivity, and in open space), I have to tilt the sensor up almost 45 degrees. Has anyone else had this problem?

The sensor's product page: http://www.maxbotix.com/MB1240__XL-MaxSonar-EZ4.html

(The forum wouldn't let me post a link in my first post)