one wire Alternator and voltage regulator question

Although the ammeter is absent we can assume with 13.8 V at the battery positive, its getting recharged slowly.

If you take a voltage reading at the alternator output terminal (stud) and compare with the battery reading, you'll know if there is a resistance to flow between the alternator and the battery. Also look what the dash voltmeter is reading since its probably tapped into a keyed circuit. In theory they should all be the same. In reality current flowing through wires and connections encounters resistance. The result is loss of energy -> that is, voltage drop.

Side note:
Ignition voltages on the coil side of the resistor all make sense.
The reason its 9.4 to 10.9 volts when starting is because starter is sucking a lot of energy from the battery during start.
If you measure the battery voltage during start you'll see the voltage drops significantly.