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There's really no way to make the charge completely ignore a vacuum signal from the adjacent port in a pair (2,1; 5,7). As velocity goes up and the divider wall gets longer the effect will decay but not to zero.
This means, in a practical sense, that this is not really 8 identical cylinders but instead 3 different classes as to intake port characteristics:
1. "neutral", more or less getting the same charge mass as other Class 1: #3, 4, 6, 8.

2. "leading" cylinders of a siamese & sequential firing pair: #2 and 5, which have their vacuum reduced as their trailing partners' valves open.

3. "trailing" cylinders of a siamese & sequential firing pair: #1 and 7, which have their intakes open too early and disturb their partners, but otherwise appear to function like Class 1.

The adjustment, so far only tested and published on the Mini (B.M.C. "A" Series) L4 by Vizard, is done by increasing the LSA and retarding the entire intake event on #1 and 7.
Doesn't this whack these? Yes, but the net result is positive. The loss on #1 and 7 is less than the gain on 2 and 5.
How much? Perhaps 2-3 degrees LSA.
The Mini intervals are very different. I suspect some Chevy L6 tuners have done this, but aren't talking.

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Good explanation of what is going on, I knew that in my head but could never have explained it that way