Imagine a sine wave feeding one coil in stepper. Imagine another wave (same but delayed 90 deg) feeding the other coil. That's how Alan's 4.0 works.
There isn't anything wrong doing so, but there's a trick getting a bit more torque in the areas where none of the coils are fully energized. I read about it in an application note.
The trick is having both coils at +100%, and then adjust current on first coil down to -100%. Then adjust second coil current to -100%. Then first goes up to +100%, and after that second goes up to +100%. We're now back to where we started.
Total current increase at 45 and 225 degrees is 20.7% (sqrt(2)/2). I suppose torque is raised equally, 20.7%, at these two points.
Note: There's no such thing as a free lunch. The extra torque is more current, which means heating up stepper a little (~7% more dissipated heat if I did my math correctly).