I had the absolute worst luck ever with binding. Honestly, I'm in awe of some of the guys here--especially the ones with large chests--that end up looking naturally flat.
Mine weren't gigantic (a C, I guess?) but they were dense and perky as hell. I could never get them to 'separate' long enough to tuck them anywhere. Flattening them outright only made me look like I had overly gigantic pecs at first that slowly devolved into a uniboob as they started inevitably snuggling. The 'binding for bigger guys' tips never helped me because I was stuck with the hourglass shape and relatively thin. On the flipside, the methods the guys were using for their small a/b cups didn't do **** for me, either.
I'm sorry I don't necessarily have any advice, but if yours are anything like mine were, that could also be why you're having issues. Your breast tissue breaks down after binding for a long time which probably helps them stay in place longer. If you've just semi-recently started, their density could be working against your efforts.