I must apologize. I did not disclose the fact that a top cover was not included in the purchase of my enclosure, and my temps are achieved while going topless.6 inches tall, 10 inches wide, approx 1 1/4 thick. Old Astron 50 amp DC power supply.
Have you tried a second test with a solid panel (cookie sheet, cardboard, whatever) place over the top for comparison. It seems to me that Imperfect as it is, simply sliding the panel over to allow a 5%, 10% etc opening may be helpful in laying out/buying a permanent lid. CheersI must apologize. I did not disclose the fact that a top cover was not included in the purchase of my enclosure, and my temps are achieved while going topless.