Yes it's a linear relationship, indeed.
Right now, you're in a position to look at details that may have a significant effect.
Are you using the rotor from October (saw blade)? Just one or do you have two?
If you tested with just one, then adding another disk will do much more than double the voltage.
And the thickness of the saw blade - that's another factor.
The rule of thumb is that the steel backing the magnets should be as thick as the magnets.
Did you measure AC volts, or DC volts? Big difference. Especially considering that many multi-meters will tell LIES when you give them wild AC.
If you rectify the AC from the generator you can have much more confidence that the DC volts reading is reliable, even on a cheap multimeter.
Did you connect your coils in Star or Delta? With 6 coils it's also possible to connect the star in Parallel, but you probably didn't.
Each of these things could significantly increase the voltage you measure.