::: comment :::
Hi champagne,
I just found a ED=11.4/1.2/1.2 rank of generation : 26 681 571 / 26 968 944 it's a very late one
but it's an isomorph of yours
I think it's the end : my situation did not change above 10.8 except for this 11.4
1 x 11.4
2 x 11.1
1 x 11.0
5 x 10.8
43 x 10.7 (including 3 diamonds, 39 pearls, 1 other)
Impossible to find a 10.9 !!!
in the 26 968 944 generated sudoku (valid minimal - isomorph verified) I've rated less than 8%
2 011 936 full rated
1 994 663 by fr (my own rating software that can go up Dynamic Cell Chains)
17 273 by serate (these sudoku needed nested level rules)
The difficulty of your pattern is the ratio of sudoku that are in the range of nested levels ~about 10% !!!
if there is no improvement today, I will stop generation and rating this evening !
usually I never generate more than 30 millions sudoku for a pattern ...