I hope I answer some of your questions below and don't complicate things even more.
If you read my document here:
https://www.vintage-radio.net/forum/...ad.php?t=86262 on the AVO VCM internals you can read about the 0.52 fudge factor in chapter 2.3 for the CT160 and Appendix 3 for the Mk IV and you can also read about the two negative half periods on the grid control in chapter 2.1.4 and why the circuit was changed in the CT160/A.
The "fudge" factor is nothing else than a way of choosing components to produce a delta voltage on the grid that corresponds to the mA/V setting on the scale, it has nothing to do with AC, DC, Mean or RMS voltages at all, it is just a factor. This delta voltage should position the needle on the 1mA/V position on the scale if the valve under test has a mA/V reading that corresponds to the setting on the mA/V control.
The two negative half wave periods, which were split up in the CT160/A to two separate signals, is used for calibration purposes as well as for the Insulation and Leakage tests.
In the Taylor series of valve testers the cathode resistor is shorted, after the standing Anode current has been backed off, when the mA/V reading is taken. The Taylor testers use two different cathode resistors, one for each range, and they have been chosen to produce a mA/V reading on the scale. You can read about this design in the Taylor 45D and 45D2 manuals where this is described in chapter 11. Taylor talks about changing the bias of the grid volts/cathode circuit when shorting the cathode resistor to produce a grid volts change, this bias change is done since the grid volts control is in series with the cathode resistor, there is also a circuit that shows this. The AVO VCMs do it in a similar way but the circuit is more complicated.
Using a scope to look at the voltages will let you see how they are changed when making a mA/V measurement in each tester, don't forget to use an isolation transformer or battery operated scope so you don't form a ground loop that destroys the scope or tester. You will have to connect the ground electrode from the scope to the correct common ground point in the tester get correct readings though!