I shaved both, namely where the grille clips into the bumper. I didn't go completely through the clip, but I'm sure I weakened it some. Even so, there's enough intact clips that I'm not worried about anything coming undone.
I wish I took pics of the bumper interior when I did it. But here's a few of the finished work.
I like the stealth look:
View attachment 30197
You can see it better if I get level with it:
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This is a close-up of where I shaved the driver side. You can't really tell that I did anything, even this close.
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And with the flash on. It looks like I trimmed a lot, but I really didn't. From the bottom of the grille to the top, it flares out a bit, so no need to trim above the bottom-most grille.
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Hope this helps!