The average voltage produced by a turn in the coil will depend on how much flux it can enclose.
A turn will enclose maximum flux if it hass the same pitch as the magnets themselves, in other words if it runs down the centre between th two magnets, or equally runs down the centres of two magnets when the magnets move on to there..
Of course you can't fit all the turns in the same place. Turns that are smaller will catch less flux but they are also shorter and so add less resistance to the coil. And so long as they are as big as or bigger than the magnet face, they will catch most of the flux that is going.
If you are winding single phase, then it makes sense to wind coils whose maximum size is the same as the magnet pitch. This allows you to put one coil per magnet pole. Inner turns are less productive, but they can be quite short. However, as the turns start to enclose a space narrower than the magnet face you have to ask whether it is worth the extra copper resistance beyond a certain point.
If you want to keep the hole in the coil as large as the magnet face then you can't get a lot of turns into a single phase stator. Depending how far apart the magnets are, you have much of the space becoming a no-go area.
3 phase is easier. YOu can make coils that have all their turns outside the magnet face (and inside the adjoining magnet faces) so as to capture as much flux as possible. You can then move them together (changing the phase) so they touch each other and maximise the utilistation of space in the stator disk. I like 3 coils for every 4 magnets.
In fact if you overlap the coils you can make them use up all the space but I find this makes them very long (more resistance) and also rather complex to assemble.
You don't have to have just 3 phases, by the way, you can have 4, 5 etc as desired just so your coils all fit in the mould.
