a storage shelf??? The spot in question is the rear "shelf" that's available when the top is up. It looks like there's indentations, sort of like pockets on either side of the shelf.
Also, I've seen some advertising for rear shock tower bars. Where would it be installed on the S? In that shelf area? Kinda looks like the top of the shocks would be about in that area. Anyone with a shop manual care to expand???

 

For anyone who thinks the inside of the rear window of an 02 is a bitch to clean,try cleaning the area Menus is speaking of.I cleaned it for the first time since I've owned my car and it ain't that easy.

 

Under the shelf is the fuel tank, and under that is where the rear STB lives (although this car is double wishbone so STB is a bit of a misnomer). You access from the boot by removing the trim. Pull out the spare tyre cover and you can see it.

 

The indentations in the tray are to allow the top mechanism to fit when the roof is lowered. Don't fill them with anything that you don't want to be crushed when you put the top down!