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To increase temperature and heat a smaller area for eggs, pizza, hard-boiled eggs, etc. use a "PIZZA BOX" for the oven box. The rest of the project remains the same--black spray paint inside, 1/8-1/4" glass sheet over top of pizza box, and aluminum foil on the top of box for light refraction into the box, using an arm prop like a dowel rod to keep the box up. It could take 2 hours for an average meal to cook. Warmer day and stronger sun - faster cook time.
Many thanks for the experience and insights on using soda cans with water to improve thermal mass for longer slow cook times, or no thermal mass to rapidly increase temperature with LARGE ALUMINUM FOIL cardboard with surface area of 4 feet.