Great question/observation.
From a mechanistic viewpoint being rotated further back around the bottom bracket in a road position should allow you to put more weight down onto the pedals. The reason is you are pushing downwards against more of your bodyweight you can even add more weight by pulling up on the drops. This must be great exercise for your legs. Riding on the roadbike would be good for muscular endurance and power development.
If you are rotated forwards into the aero postion more of your body is supported by the elbows and less is available to help you push down on the pedals so being in the TT position is probably not as effective if you want to develop your power on the bike.