An ellipse is a plane curve with two foci which is symmetrical on both the vertical and positive axes, and intersects with these axes perpendicularly.
I recently heard a student tell another one, “She means not a racetrack and not a football.” Works for me, as long as it’s symmetrical both ways, as below.
Use that boring old method, a pencil held up in space, to measure the distances above the bowl's ellipse and below it. You'll be surprised at how often the bowl has very little showing below the rim, and a lot above the rim.There is nothing like a contour drawing to check your composition. This is not time consuming, but the most important work you can do. The mantra of my studio is, "draw slow, paint fast" (and thank you to Rhea Horowitz for coining that). It's a lot easier to correct mistakes in a pencil drawing than in a mush of paint.