So, all in all, you've done a pretty good job, and are entirely in line with what this challenge demands of you. Starting with your cylinders constructed around arbitrary minor axes, you've done a great job of going through and analyzing the minor axis alignment of each ellipse. That isn't rocket science of course - but you're demonstrating the appropriate patience and fastidiousness in doing so, and aren't letting yourself get distracted by situations where your alignment may have been off by just a little bit - enough to maybe argue that you were close enough, or worse still, for your brain to trick you into thinking that it was correct. After all, it is pretty easy when the initial minor axis line is sitting there, to think that a one or two degree deviation isn't really present.

Now, one of the things I like to leave for students to pick up on themselves through this section of the challenge has to do with foreshortening. Sometimes students don't realize this on their own at all, whereas others - yourself included - seem to understand it somewhat intuitively, but perhaps don't understand the specific mechanics behind it.

Basically it comes down to the relationship between two elements for foreshortening. You've got your normal scale shift - far end gets smaller overall than the end that is closer to the viewer. First grade stuff, really. Then you've got something people don't necessarily think of as an aspect of foreshortening - the degree shift, where the far end of the cylinder has a wider degree than the closer end. Of course, we know that to be the case, as it's stated plainly in the instructions, but we don't necessarily always think about how and why the shift should be minor or significant.

Basically, if you have a dramatic foreshortening (usually where the cylinder is very long or very close to the viewer's eye) you're going to get both a dramatic shift in scale from one end to the other (far end gets much smaller), as well as a more dramatic shift in the degree (far end is much wider, proportionally speaker, than the near end). Conversely, if we have shallow foreshortening, we have only a minimal shift in both areas.

At no point would we end up with a dramatic scale shift and a shallow degree shift, or vice versa, because they're caused by the same property. Now, as I said, you demonstrated an intuitive grasp of this concept at the very least, and you maintain this relationship between degree shift and scale shift throughout. So good work! It means your internalized grasp of 3D space has developed very nicely thus far.

Moving onto your cylinders in boxes, yeah - it's true that you have a tendency to have lines that should converge towards the same vanishing point instead pair off (with the lines of each plane converging together, instead of all 4 converging to the same VP). So yeah, you need to continue working on that, but it is really not that surprising. It just means that you probably weren't working on that much in a while in your warmups, or that your focus wasn't in this area. Consider this a reminder to do so.

The bigger thing about this particular part of the challenge is that it's actually a lot more about the boxes themselves than it is about the cylinders. Specifically, it's about learning how to draw boxes that have a pair of faces which are proportionally square in 3D space. You know how until now, all our boxes have been pretty arbitrary with no specific proportional requirements - but if you want to draw a cylinder inside of a box, then the ends of that cylinder need to be enclosed inside of actual squares in order for the ends to be circular (in 3D space). Therefore, the cylinder itself becomes just another aspect of the correction phase, just like the line extensions. If the minor axis of the enclosed ellipses align with the given set of edges in the box, and if the contact points of each ellipse with its enclosing faces similarly align towards the other sets of box edges, then you've got yourself a hand some little box with a pair of squares for faces. If not, then it's more likely that the resulting cylinder is being squashed.

Keeping this in mind, I definitely think you've improved a great deal in your intuitive ability to construct such proportionally square boxes, specifically by going through the process again and again and attempting to tweak your boxes (both consciously and subconsciously) to better fit the requirements of the exercise.

Stepping back to the sets of parallel lines converging in pairs for a second though, just remember to always focus on where that vanishing point is going to be, specifically by thinking of all four lines of a given set. It's a lot harder than we make it sound when we instruct students to do that in the box challenge, because it often means thinking about certain lines that have been drawn (and therefore are cemented) and other lines that haven't yet been drawn (and therefore can be altered in their trajectories). Always think about their relationships with one another at the vanishing point, and remember that the longer your box is, the sharper those convergences are going to be. As our boxes get longer, we tend to focus our dramatic foreshortening on the length-lines, the ones that define just how long the box is - this is why it's easy to forget about the fact that the convergence of the other two sets of lines may also need to be much more dramatic. We focus entirely on the length, to the detriment of all else.

So! All in all, you're doing pretty damn well, and you've got a good grasp of how to draw ellipses in planes, how to think about minor axes and the foreshortening of your cylinders, and you're getting much better when it comes to your intuitive grasp of the proportions of your boxes. Keep up the good work, and consider this challenge complete.