The two surviving Iron Brigade hats are both still "standing tall," if you will, and kitted out with bugle, hat cord and eagle, with the side turned up. In the 7th Wisconsin, there is photographic evidence of wearing the hat with the cord and brass, but with the brim flat all the way around. There was a tendency to punch down the crowns into a "cowboy hat," but this shows up in 1864 photos, and is mentioned in brigade memoirs as a spring 1864 habit. (I'm not saying it didn't occur earlier, but the boys themselves noticed it as a departure from previous practice.) I've never seen evidence of telescoping in the Iron Brigade hats. Granted, that doesn't speak for the entire AoP, but only the unit which considered the dress hat their signature item of appearance.
Pine River Boys, Co I, 7th Wisconsin
"We're... Christians, what read the Bible and foller what it says about lovin' your enemies and carin' for them what despitefully use you -- that is, after you've downed 'em good and hard."
-Si Klegg and His Pard Shorty