On a second glance to your original organic forms with contour curves, I can actually see some shifting of the degree. My mistake - not sure whether my eyes were playing tricks on me in that moment or what, but I apologize.

As to the other question, both are technically correct, in that the top one follows the same trajectory of the fuller contour ellipse. It is however very common for students to, when not thinking about the full ellipse at all, draw a much shallower cut across the silhouette, which flattens things out. This is something that can happen due to simple carelessness or a lack of focus, but it also reinforces itself through repetition, which is why I encourage students not to use this approach when drawing organic subject matter within this course. We do delve into more subtraction in Lessons 6 and 7, where we deal with geometric structures - but in the interim, strictly working additively will be more beneficial, as it's easier and contributes to the overall spatial understanding which in turn makes the subtraction more reliable and successful.