And, you'll find other toilets that have similar arrangements that do the same thing with the tank, and actually work fine! They all have more water in the tank than they flush. IF yours doesn't work well, it is design fault. If you hold the handle down to empty the tank, it might work better, but then you'd be using maybe as much as twice the water it is legislated to use. The fix is not a new flapper, it's a toilet that actually works with the legislated water volume.