Helmet buffeting is one of those things that has to be solved on an individualized case by case basis. I've gone through three different windshields and mounting them in every way imaginable to try to get a smooth, clean ride with clear air and no increase in noise and buffeting. It's embarrassing how much time I put into it. But what I can tell you is that the angle makes a huge difference, your height makes a huge difference, the height of the shield makes a huge difference, and venting/MadStad style makes a huge difference.
Unfortunately the Harley shield doesn't let you adjust pretty much anything; you can't change the angle and it doesn't have vents. You can actually adjust the height a little; I'd recommend trying pushing it as low as you can get it. The most ideal situation I've found so far for decreased noise while getting the wind off the chest is with a steeply raked shield that's quite low, it pushes the wind up off my chest but lets the helmet ride in clean smooth-flowing air. I couldn't get the Harley shield low enough for my taste, but you're quite a bit taller than I am, so perhaps you'll find a satisfactory solution with the shield at its lowest possible position. If that doesn't work, try raising it. You can raise it higher than Harley says, if you slide the turn signals down the fork a few inches you can mount the top windshield bracket above the turn signals.
What I found helpful was to try to gauge the approximate height needed by standing on the footpegs and raising my helmet up an inch at a time, to find where it needed to be to avoid the bad air. If you find that you're just an inch or two away from bliss, you can always try cutting the windshield height down a little (assuming that you can't get it to that point by just mounting it at a different height on the forks). Good luck!