You might find the answer here:
http://mitrocketscience.blogspot.com/20 ... r.html?m=1
with 12 slots you have 30 mech degrees between each slot.
10 poles is 5 pole pairs so 30 degrees mech is 5*30=150 degrees electric
So hall sensors are 300 degrees electric apart.
As the distance between the sensors can be multiplied with integer values without changing anything then they fit a 5*60 (=300) degree hall setup.
flipping the middle/third sensor means its inverted (it's position is then offset by 180 degrees electrical). A flipped sensor also means hall signals changes from 60 degree to 120 degree setup:
https://www.parkermotion.com/dmxreadyv2 ... estion=175
You can confirm above by assembly of the motor, rotate the rotor and measure hall states. If you have positions of 111 or 000 (all sensors on or off at the same time some angle during the rotation) then it's 60 deg, otherwise it's 120 deg.