You need to get an intuition for the cube in perspective first. Like the others mentioned, you're doing some random box - you need a cube first. Or you know a square if we're talking about one face only. I recommend you use a free 3D app like Blender and experiment with different camera focal lengths because they affect how distorted the perspective is. Draw them free hand as you reference the cube from the 3D app and check to see how far off you are. That's how you get the intuition for it. Good luck!

I don't quite understand but it seems to me that what you want to do is not an ellipse in perspective but a circle in perspective. So, I'm attaching a little sketch I made in a hurry and it's rather ugly, just to help me with the explanation (I've always had a bad technical stroke, even using a drafting table, let alone a ballpoint pen on a notebook, considering that I'm not used to drawing on paper anymore. I just don't feel like opening photoshop right now! 😅😅) OK, when you want to draw a figure in space you have to make sure you have as many reference points as possible. Therefore, as you have rightly guessed, you have to start from a square, in which you will inscribe the circle (a circle whose circumference will have to touch all 4 sides of the square, which is not the case in your drawing), only in your drawing the construction of the square that should guide you is already wrong. So, first you will draw a square in the plane, inside which you will draw the circle. Then you will draw the vertical axis, the horizontal axis and the two diagonals. In this way you will have 8 reference points. You will draw the vertical points on the line where the observer is positioned (I don't know what it's called in English, basically the horizontal line at the bottom of your perspective plane) and the vertical points by means of 45 degree projections, as you can see in my (ugly) sketch. In this case we have two points of view: towards one the vertical points will be directed and towards the other the horizontal points. At the points where they meet you have the 4 corners of the square, which you will use to determine the diagonals and thus find the centre of the square. Using the centre dividing lines and diagonals, you will then construct your circle in perspective, making sure that the circle touches all 4 sides of the square. It requires a bit of practice but this is the procedure for 2 point prospective (Keeping in mind that my sketch totally sucks! 🤣🤣🤣)

One of the things Scott Robertson talks about in his book is using ellipses to estimate a cube. In other words, draw the ellipses first, get them placed, and then draw the cube around them. Your ellipses look like they are in correct perspective. They are just too far apart.

Hi @Samuel Eli, i went through Marshall's perspective course recently as well. The first thing i noticed was that the box you drew is not a cube, the length sides are larger than the height of the box. This means that if you want to draw a perfect circle in one of the side planes the circle will touch the top and bottom of the rectangle, but it will not touch the left and right side of the rectangle. So i think the construction of the ellipse is fine. Try doing it on a more perfect cube in perspective and it will work out better. In the beginning of Marshall's classes he eye-balled/estimated a perfect square in perspective, in the last class he actually provides a method to draw perfect squares in perspective (Planned Projection). Hope this helps

Is it just that the box isn't a cube in your example? If you are trying to make the circles fill the box face, it will be distorted (a flattened cylinder) if the box is rectangular. If this is the issue, then just look up drawing a cube in perspective to see how to make sure the surface is equal within the perspective lines.