Alright, here is the rest of what I have to work with. I hiked up the Matrix this weekend to snap some pics of the bottom.
Even with the two front grill blocks, there was still the area between the bumper cover and main support that was open. This will need to be closed up.
This is the area I'd like to go over with aluminum flashing between the two support members. The only thing I don't like about it is the aluminum flashing may rub the exhaust as it hangs down a bit below the support member's lowest level.
This is the large drop off between the engine bay and passenger compartment. Definitly not good for keeping airflow attached.
Moving backwards you can see that the floor of the car actually tapers down towards the back of the car.
In these next three pictures you can see Toyota did seem to try to use some underbody panels for one reason or another.
However, once you get beyond the rear axle, all bets are off. There is nothing here to help airflow. Thankfully, the bumper cover doesn't hang down real low. So, there isn't much parachute effect going on.
