Here is a Very simple Experiment for you to try at home.
Most of us have a Stereo Sound system at home with detachable speakers..
Place one speaker to your left and one to your right.. at equal distance from each other...
Place your head at the same level as the main woofer of the speaker in between both speakers and the sound should appear Directly infront of you where there is no speaker..
This is how to achieve a correct sound stage.... The music should appear to come from directly infront of you...

In a Car this is hard to achieve as you are not seated central and because you are not going to be seated of centre the speaker nearest to you will alway sound louder..

With the Typical 3rd gen Magna ( TE-TH) the front woofer is mounted low in the door on each side the Ideal Listening position would cause an Extreme amount of discomfort because the Ideal listening position is where the centre console is just a little behind the Gear selector... trying to drive sitting here would hurt as well as being illegal..

To Reduce discomfort and try to level the sound stage The Ideal Speaker set up for the 3rd Gen Manual is Either a Set of Splits ( Seperate woofer and Tweeter) or a Set of Co axial Speakers( a Woofer with a Tweeter mounted Directly above it)
with an Adjustable Tweeter so it can be angled up wards and aim the sound higher then the centre console where you have a chance to adjust the sound so it reaches your ears...

(My Keyboard Batteries are running Flat If anyone wishes to cover a Point I have missed feel free to cover it)

Actually in a car i find it's better to have the soundstage with the centre being in the centre of the dash/windscreen. If you aim to have the stage directly in front of you, yes it will sound good, but it will mean the right side of the stage is all compressed into a tiny space and the left side is spread out. If you try to have the stage spreading from the far edges of the car then u will get a much better sense of stereo.

So more like you're listening to concert, just ur on the right side of the audience slightly.

The head height rule is a good target to aim for, although I know some people (eg FHRX) prefer to sit above his stage and peer down on to it, so this can be personal preference. I try to get as high as possible though

If anyone has a chance try and pick up some testing discs.
Sheffield labs - Autosound 2000, alpine f1 status first encounter and so on. These are a wealth of info.

There's a great track with a person walking across the stage tapping a drum at equal intervals, it is perfect for setting up the stage width.

Staging is one thing many people dont think about, but a well staged system adds that extra bit of realism.

Peace

Tim