Nice problem! However, you wrote:
It is not that 21pt anchor is much worse than 20pt anchor, it is just due to the fact that Black achieves more when hits on a higher point and White fails to hit back.
I'm not sure I believe this theory. For example, in the position below, GNU 4-ply thinks that making the 20pt and leaving an outfield blot is tied with making the 21pt and the 11pt. That indicates to me that the 20pt is noticeably more valuable than the 21pt. In this position we can't argue that what's going on is that a blot on the 20pt is more vulnerable than a blot on the 21pt, because there is no blot on the 20pt.
The score (after 0 games) is: gnubg 0, tchow 2 (match to 4 points)
| gnubg | 161 |
|---|---|
| |
| tchow | 160 |
Position ID: 4PPgASjgc+QBCg Match ID: UYmIAAAAEAAA | |
| # | Ply | Move | Equity | |
|---|---|---|---|---|
| 1 | 4 | 22/20 21/20 | -0.063 | |
| 0.545 0.122 0.004 - 0.455 0.076 0.001 | ||||
| 2 | 4 | 22/21 13/11 | -0.067 ( -0.003) | |
| 0.556 0.137 0.005 - 0.444 0.089 0.002 | ||||