I'm putting together a rear parcel shelf with the original pressboard. The two lower pieces (the bump and the piece that goes behind the rear seats) are in good shape. Just had to put in a few staples. The piece under the rear window needed to be recovered and I got a new matching piece of vinyl (matches the bump and is different than the lower part).

The foam under the original material for the under the window piece had essentially turned to powder. I'd like to know whether this foam (of which I also have a replacement) is trimmed to just fit the top of the shelf or is it supposed to wrap around by about half and inch like it does on the bump part ?

TIA
Ravi