I used to ride my old FLH without a windshield and always with full face helmet. I rode with sunshades and without and didn't have any buffitting of my glasses or eyeballs.
I modified my frontend to accept the quick disconnect RK windshield. I had a full height, 19"?, and it would force me to look right through the very top of the shield and it was very hard to ride on winding roads as the top was half way between under or over my viewing line of sight. With this height shield I had no buffitting at all.
Not thinking much about it I've cut that one down about 3" and now when I'm riding on the road the top of the shield is just about at the ground of the vehicle I'm following. This solved all my curving road issues with the shield causing viewing issues, but now my helmet really buffits. With or without glasses my eyeballs shake.
If I dip my head a few inches down, the buffitting goes away.
I've just learned to live with it for the past couple years, although a fix would be great.
I'm thinking the tiny deflector that will be coming with my new SERK, as some have said, will do practically nothing to get the wind off me.
So I'll be looking to just drop my FLH assembly on it and see what happens.
I'll keep following this thread with the hope that something OTHER than the lower deflectors are the answer.
Thanks for all the information so far.