Originally Posted by
Retro Grouch
Sometimes the devil is in the details.
For indexing to work properly, the derailleur has to operate in a plane that is exactly parallel to the cassette cogs. 11-speed cassettes pack 11 cogs into roughly the same amount of space that an 8-speed cassette only has 8. Since the cogs are closer together smaller amounts of misalignment will have a negative effect on your indexing. I suspect that the more precisely you can get your bike's rear triangle, dropouts and derailleur hanger aligned, the more reliably your shifting will index.
That was exactly my thought. With 11 speed, it has to be so precise that bikes straight out of the box sometimes need aligning. I already planned to have the rear end spaced and aligned so it's more convenient to swap wheels, so it ought to be perfect. I just got back from a ride with the bike set up with 11 speed, 130 wheel just shoved in. It worked fine, but there are a few shifts that would be marginally better with alignment.