For best aerodynamics, try to keep your handlebar/ knee clearance at a safe minimum… just a half-inch clearance is enough for most riders. Keeping the knee to handlebar clearance as low as possible will give you the best view of the road, and also keep your handlebar profile as close to the top of your shoulders as possible to further reduce your frontal area and aero drag.
Also, try to adapt to the most straight-arm position possible if you are interested in the highest aero efficiency. The form of your arm should replicate a fist punching a hole in the air, creating a straight arm and allowing the shoulders to be at the lowest possible position. This is the ideal position for reducing frontal arm area using your steering position.
Many riders who came from years of traditional recumbent “praying mantis” or “begging hamster” arm positions find a little strange at first, but come to like our “superman” position over all the recumbent steering geometries! Our handlebar geometry allows for minimal steering “tiller”, locking the steering column to the rider's shoulders, contributing to increased steering stability.
To reduce air drag, take a look at seat angle, steering and arm position, wheels/ tires/ forks, and other considerations.