I wish you would share with the class what you're smoking.
All you do is just add a threshold for the flat tax - duh. Anyone making X and up - pay Y%.
Besides how the hell are you going to lose 1/2 your income if you're not paying 50% tax? i.e. Go with the meme "if 10% is good enough for God, it should be good enough for the government." You make $100? You owe $10. You make $50? You owe $5. Even if you make $10, you owe $1. At no point are you going to lose 1/3 to 1/2 of your income unless that's what the percentage is set at.
And let's put it this way: If you make taxes too high, then it becomes a big incentive for the well off to cheat (and I mean ACTUALLY cheat on taxes, not just using loopholes) because then you're getting a substantial reward from it. If the tax is flat, revenue tends to go up because then it's not that much of a gain to risk cheating, so people just go ahead and pay.