I wish I had a scanner, as I would just scan the article for you guys. The following is some paraphrasing I did from the article:

All this study was done for running in the SCCA Trans Am series. They new speeds would get up to 140 mph on the track and Chevrolet wanted to be certain the Camaro would stick to the track. It was Chevrolet's experience that production cars tend to exhibit front end lift which becomes excessive at high speeds. The Camaro was studied using a scale model in a wind tunnel to determine the base aerodynamic qualities. Then they experimented with various sizes and once the best combination was found they had their style group re-work from a styling point of view for what be put on the Z/28's.

To verify Chev's claims Car Life magazine performed a series of tests on a '69 Camaro with various spoiler configurations. The charts they created, (where I pulled the numbers I posted above) were printed in their June '69 issue.