Try cutting at the 2" setting. I'm not impressed with mine at 3.5" either. Try it at the 1/2" setting too, you may be surprised. At 1/2" mine cuts probably 2.5" or so. Yours may vary but this is mine on the 1/2" setting. You can see how high the weeds were to start:
Shaeff, thanks for letting me know the cutting height adjustment only loosely relates to actual cutting height. I couldn't imagine anybody actually cutting at 1/2 ". You'd be hitting rocks and dirt constantly. I'll readjust the height and try again.
When encountering the really heavy stuff like in your photo, Mine choked out and stopped. My neighbor clutched it quickly and I didn't hear any squealing belts. He backed it out, raised it up, when PTO was re-engaged it cleared and ran fine. I think his groundspeed was too fast. Soon I will be back operating my own tractor and I will learn a lot more then.
Typically, does the flail have to be operated more slowly than a bush hog?