"To clear up some misconceptions, if you increase the weight of the counterweight and bring it closer to the pivot, eff mass will decrease with the change of distance."
That's only because eff mass will vary as the SQUARE of the distance between pivot and CW center of mass, whereas the relationship between eff mass and CW mass is first order. I'm writing this, because I don't know where there was a misconception. One interesting thing that falls out of the equation is that if you use a relatively low mass CW, you can have more control of eff mass simply by sliding the CW toward or away from the pivot vs using a "heavy" CW. I think this is what Technics (and other makers of vintage Japanese tonearms) had in mind with their design of the EPA100, which they claimed could be used with cartridges that vary widely in compliance. Modern tonearms have tended to go in the other direction, with heavy as possible CWs mounted close as possible to the pivot, to reduce inertia, I think. My Triplanar came with a variety of interchangeable CWs, so the CW can always be close to the pivot. But look at the very expensive Durand Telos tonearm; it has a rather long rear projection and a relatively light CW compared to some others and even to the Talea.
