...so, KOPS, was (and can still be) used for a 'ROAD bike' start point. Back when there was little/no science related to 'position'.
It is directly, immutably tied to saddle height ON A ROAD BIKE with geometry close to traditional road and rider use.
Rider/Coach would set up saddle height, flatten/level the saddle and then set the setback; discuss and deal with reach/stem length. Then 'tune' from there, over a period of minutes thru weeks; maybe even longer.
Ischial Tuberosity became part of all this because, the 'knee' is quite wide/long. It's just a 'std spot', not any scientific thing. A standard spot. Without that (as OP noted) it could be most anywhere on the knee.
A 'start point' for what has, and still mostly is, a common 'road' position.
I would NOT suggest that it works for any other setup (it might - don;t know... don't care)
The OP never noted WHAT they were trying to use KOPS for... and is gleefully enjoying the result of their OP.
I would not think it's used for current mtb, and certainly not DH or Enduro, maybe XC? Certainly not for TT or TRI with a TT setup.
... do we think KOPS or balance works for a cruiser ? maybe a 'Bent' ? CX or gravel? aaahhhh, something we can argue about! LOL!
the whole for/against KOPS/BALANCE is sadly, very lilliPUTIN/Big-Endian...
start somewhere, ride, figure it out.
Ride On
Yuri