Yes, that part of the pitcher is called hip, and it seems that while some species have a stable hip in the middle or lower part of the pitcher, some others have a hip that can be in the middle or along the whole upper part and even absent, that giving a rounder shape to the pitcher.
A curious thing that I would like to understand more, is that "mirror" species like andamana-suratensis, kerrii-kongkandana, mirabilis-var.globosa and probably others seem to split one from the other by using that feature, I don't know why.
Plants of var. globosa have been classified in grades depending on where the hip is, but that's a horticultural thing, as "the upper goes the hip and the better the pitcher looks"
It has nothing to do with taxonomy, as in the wild you can find var. globosa plants with hip in all positions, randomly going from the middle to absent.