Hmmm, I'm a petite female also and ride an Aegis Swift with a very short top tube also (19.1"). I also ride in the drops a lot and have never had my knees brush my handlebars. It's possible that your stem is too short. I use a 90mm stem which gives me about a 45 degree forward angle (my back) when I ride in the hoods.

When you're riding, look down at the front hub of your front wheel, and if you can see it while riding with your hands on the drops, you probably need a longer stem. Normally, you want the front hub to be hidden by the bars when you're riding on the brake hoods. My bike originally came with a 70mm stem, and I changed it out for the 90mm when I discovered the bars were behind the hood in the position I described above. I have found that my back is actually happier being slightly more stretched out too.

Another plus of a longer stem, if you happen to have a shorter one now (< 80mm), is better bike handling in front - less twitchiness.

One other idea - if your stem is the right length and not too short after all, you could possibly rotate your handlebars up a bit (i.e., to bring the brake levers higher), which will result in the ends of the drops moving farther from your knees. You might want to consult your LBS for a fitting as well, especially if you are unsure about all of this.

Good luck!
Emily