Clues to clean behind GS rear mesh?

[BL330]

Spring will be here shortly and this weekend was not the usual brass monkey weather, so I got in and washed, clay barred and polished the GS. Awesome result to freshen up the shine but the area behind the rear grill is noticeable. It remains non shiny, even though I threw suds at it and hosed it. I just can't get a chamois in there to wipe it.
Maybe this is only noticeable with light coloured cars.
Does anyone have a clever technique to clean this ?

 

[EnzoMC]

one option is to spray APC/ degresser and let it soak then rinse off ( don't let it dry) or as I do with a long thin brush with APC between the vent clean the area then apply a spray cover.

for shows I would remove the under cover and clean / protect

 

[safrane]

Front grill?

If so its only 6 hex head bolts.

I remove mine every few months and use Armor-all to give the air ram a decent gloss after a wipe. I also use a non acidic wheel cleaner to remove the tarnish around the chrome and trident.