Voltage generated by individual coils goes down the larger the number of coils

Question

I'm trying to make my own alternator & study the physics behind it.

So I have a circle of magnets rotating over 4 coils, forming a square (90 degrees each).

When I remove 3 coils from the square and only rotate magnets over 1, the coil produces ~6 volts AC.
However, with 4 coils, each coil produces only ~3 volts AC.
I even tried with 8 coils (in a circle configuration), and they seem to generate each ~1.75 volts AC.

Why is that?

More infos:
The coils are connected in parallel, not series.
Each coil has between 30-40 ohms of resistance.
They are very close to each other (~ 5 mm of distance between 2 coils).
Their winding are all in the same direction, and the magnets all have the same polarity.
The coils are NOT connected to a load, only to a multimeter (1 coil at a time).

Update:
To clarify: I test the voltage 1 coil at a time using 1 multimeter. Thus, the coil being tested is not connected to the circuit, only to the multi meter.

Answer 1

The coils are connected in parallel, not series.

As described, the coils will be able to produce positive as well as negative voltages so, if one coil is individually peaking positively, it might be "held-back" (or restrained) by other coils producing a negative voltage or 0 volts. You just can't parallel coils and have a sensible result unless, the outputs are all pretty-much in phase with each other.

Alternative idea; connect the coils in parallel using diodes forming a rectifier.

Answer 2

Nevermind, found the culprit.

If the distance between the magnets and a coil is event 1 mm differents, the voltage can differ significantly. (1mm adds 50% voltage in my case).

So the weight of multiple coils , believe it or not, is pulling down the plate of 1 or 2 mm.

Thanks again for all your excellent suggestions guys !