Koetsu compliance compatibility issues

The Onyx (Sugano) was a complete disaster with my Pluto 9A.
In contrast, this arm matches almost well with the Goldfinger (similar mass/different compliance). It seems its a matter of compliance more than cartridge's mass. But this is a contradiction as later, after mounting the Denon DL103 (even less compliance than Onyx) the results were also unacceptable , but better than Onyx due to the lighter Denon body.
What was really happened ?
The Goldfinger has a phenomenal trackability especially in contrast with the Onyx.
This alone was enough for me to stop trying to find a proper arm for Koetsu.
Of course those are examples of extemely wrong matching (uknown Pluto effective mass) & if you dare to test for trackability, you may aware that you have a damaged Koetsu sample.
Now with the Colibri (less than half the weight of both & 35 Cu compliance) my Pluto makes the perfect pair.
So, don't bother. You simply can't trick the formula.
The Alphason HR100 is a great arm for Denon DL304, so maybe matches equally well with Koetsu Black.
If you really like the unique Koetsu sound, you must first purchase a robust & preferably 12" arm. Then, pair them with an electrostatic speaker & some OTL power amps.
Somehow I feel that letting your Koetsu decide for your system building, maybe is a little too much love for her.
Sorry for I can't help a lot, but I value Koetsus even less than DL304 and way below the DLS1. They have much character to enjoy, but the trade-offs are many more.
Having said that,I admit that If I would like electrostatics (over horns) & OTL (over SET), I definitely give a chance to Koetsu.
It has a beauty unable to find elsewhere in the chain.

George

No one is likely to have the breadth of experience described by Syntax. However, my Koetsu Urushi, which seems to be at least a bit higher in compliance than your Black, ran well in my Triplanar (effective mass = 11 gm) but is even better in the Kenwood L07D tonearm, with the stock 12-gm headshell. I could believe it would benefit from a higher effective mass tonearm like the FRs.

Geoch, You wrote, "So, don't bother. You simply can't trick the formula."
But in fact the formula itself is "tricky" and only gives you a ballpark estimate of the resonant frequency, even if your input data are accurate with respect to one's particular sample of a particular cartridge. So my approach would be to forget the formula but to try in a general way to match a low compliance cartridge with a medium to high mass tonearm, etc, etc.

I am one who does use ESLs and OTLs and who does very much like the Urushi that I own. I also have a Colibri and an Ortofon MC7500 and several tonearms and turntables. Many days, I prefer the Urushi over all. I don't think a 12" arm is necessary to enjoy the Urushi, but when I finally acquire one, I will try it.

Just to update, I'm enjoying greatly my Koetsu with my older phantom arm. Loving the musical combo!

I'm using a koetsu jade with a VPI JMW-10 on a TNT turntable.
On paper the JMW-10 is a poor match for the jade as it's a unipivot with effective mass is in the 10-11gm range. That being said it sounds awfully good to me. Would an arm with a higher effective mass sound better? Maybe and one day I plan on finding out but for now the combo sounds great regardless of the math formulas.
A few things to consider, the stone body koetsu by being heavier by around 4gms then their wood/urushi counterparts and thus increase the effective mass of the arm their used with.
The effective mass of an arm can be increased by adding a cartridge weight. I know that VPI sells a 3gm aluminum weight for this purpose and I've seen a 5gm brass head shell weighs available.
Additionally by using a LIGHTER counterweight further back on the arm as opposed to a heavier counterweight closer to the pivot point will also increase the effective mass.
Just my 2 cents.