Took the one exception to "nothing further": the cells were cheaper than arguing. Same partition for every cell, NDCG at 10.
nprobe % of 132 cells LEMUR-2048 MUVERA-10240 gap
8 6.1% 0.32346 0.37341 -0.04995
14 10.6% 0.37689 0.42981 -0.05292
20 15.2% 0.41514 0.44816 -0.03302
26 19.7% 0.41962 0.45828 -0.03866
32 24.2% 0.44641 0.46894 -0.02253
40 30.3% 0.47122 0.48163 -0.01041
48 36.4% 0.48289 0.48723 -0.00434
50 37.9% 0.48766 0.48723 +0.00043
53 40.2% 0.49422 0.48709 +0.00713
58 43.9% 0.50226 0.48665 +0.01561
64 48.5% 0.50850 0.48939 +0.01911
exact 100% 0.54910 0.50021 +0.04889
The gap widens first, -0.05292 at 14 against -0.04995 at 8, and is still -0.01041 at 40. The sign flips between 48 and 50, 36.4% to 37.9% of cells, first positive +0.00043 at 50, inside MUVERA's own wobble, 0.48723 at 48 and 50, 0.48665 at 58, 0.48939 at 64; held at its 64 value the flip moves to 53. Call it a band, 48 to 53, 6x to 6.6x the default probe, positive above: +0.00713, +0.01561, +0.01911 at 53, 58, 64. "Toward nlist/2" starts there, not lower.
Both 64 numbers were in my first reply without MUVERA's probe count; it was 64, reproduced here exactly. Its +0.01911 gap is 2.3x your small end.
Your LEMUR-side interpolation was nearly exact: 0.37689 against your 0.37341 at 14, 0.50226 against your 0.50021 at 58. MUVERA-10240 climbs then stalls: 0.42981 at 14, about 0.487 from 48 to 58, 97.8% of exact at 64, above the 92.6% end you priced and below the ceiling.
On z, both moments moved, 20 to 40 draws: mean 0.257038 to 0.254159, down 1.12%; sd 0.011133 to 0.010501, down 5.68%. In your decomposition, -1.989 x 0.870 for the gap to the mean, x 1.060 for the sd, is -1.834: your mean branch, overshot, the sd pulling against it. The sd tightened; the record range grew by one draw, seed 71 at 0.234085. "The envelope grew" meant the range.
That closes the fourth leg; the residual stays as named.