With a 3/4" thick stator you are near optimum with those magnets. You can vary the thickness either way quite a bit with little difference in power out.
If you double the thickness you can get in twice as many turns but your flux density will be just about halved so the voltage will be very similar.
Your 1/8" clearance between magnets and stator is costing you a fair bit but with an alternator that size you most likely can't reduce it a great deal and still be safe mechanically.
With thin stators you have a high gap flux but little winding space and the 1/4" mechanical gap is a large and wasteful factor in this winding space.
With wide gaps this mechanical gap is less of an issue and within reason it pays to use a lower flux and have more winding space. There comes a time with large gaps when the leakage between poles becomes excessive and that limits the stator thickness.
As far as the magnets go it is best to work them half way up the demagnetising quadrant and for typical neo you are looking at something around 600 to 650 mT.
This occurs when the air gap is the same as total magnet thickness if you ignore flux leakage. For 1" thick magnets it suggests an air gap of 2 ". In real life it works better at something like 1.5" and with narrow magnets you may be better off with something nearer 1.25". Leaving 1/8 per side for clearance this makes your best stator thickness something like 1".
I think with careful optimising you will do a little better with this than a 3/4" thick stator but it's not going to be an improvement that's going to change the world so what you have now is not going to be far away from the ideal.
Just as the force varies as the inverse square of the distance between magnets, the flux varies as the inverse over a fair range so big gaps low flux, small gaps high flux. For a given set of magnets you have a fixed power out at a given speed and not much you can do to alter it.
Flux
