I understood that SegWit would allow about 1.75 MB of data in the average case while also allowing up to 4 MB of data in the worst case. This means that the mining and block distribution network would need a larger safety factor to deal with worst-case situations, right? If you want to make sure that nothing goes wrong when everything is at its worst, you need to size your network pipes to handle 4 MB in a timely (DoS-resistant) fashion, but you'd normally only be able to use 1.75 MB of it. It seems to me that it would be safer to use a 3 MB limit, and that way you'd also be able to use 3 MB of actual transactions.

As an accounting trick to bypass the 1 MB limit, SegWit sounds like it might make things less well accounted for.