[mhs4771]

Here's my take on the semi-closed top vent. With the cover off you should be able to see some cooling fins at the very top, thus you want the air flow to pass over those fins before exiting, without the panel blocking the lower portion of the cover the air would exit there and never reach those fins. In a non-slide fridge with the roof vent it's a non issue as the air flow goes straight up and pass those fins. I think everyone is too cheap to make a new cover for the upper vent that would be smaller. Just my opinion and info that I've read.