'Loading Random Movies' question

First off thank you so much for doing such a great job of explaining this process and the ActionScript that makes it work. I just had one question and pardon me if I missed something obvious. My movies are loading much smaller than they should. I created my source movie and made it 750px/350px which is the size of the movies I’m randomly loading. The circle symbol I made 16px/16px per the instructions. I did notice that if I adjusted the size of this symbol I could adjust the display of the random loaded movie files. I had to adjust a few times to 37px/35px before it looked about right. What’s the correlation between the size of the oval symbol and the size of the movie files? Thanks.