Totally different shape and contour. You sit "in" them not "on" them (As Molly of Molly and John "boilerupxfire") once told me.
I did not understand what she meant until I sat in a base coupe.

Next time you are at a meet, try sitting in:

• A Limited (perhaps your own since most own limiteds)
• An SRT
• A Base/SE

Also, you may observe, if you are 'tall from the waist up', that the base seats sit lower (they have no motor/drive units under them) and that his will make some of us more comfortable as well.