Toilet flapper sizing problem
First, verify that your filler pipe or flapper hinge piece is installed correctly. Perhaps it's backwards, moving the flapper mounting ears away from the drain hole slightly.
Then, I'm not sure your assertion that all flappers are the same holds water. :P Take yours to the store and compare brands for one with longer arms.
If you're the inventive type, clip the loops off your flapper and zip-tie some strips of plastic in their place (with half-twists if needed), then cut holes at the appropriate position.