What you are seeing is the airfoil reacting to dead air. While in forward flight you're making your own wind. That's not the appropriate term, but the best I can think of for now. As you slow down you want to slightly increase head speed to maintain the resistance. Even with the syms you'll see some of this, just not as dramatic. The flat blades will give you more stable flight but aren't really made for "fast" forward flight. I think for the amount of time you've spent, you are doing great. Keep it up.