You are not measuring ambient temps in your enclosure. IR guns measure surfaces not air. I often see seven degrees difference in surface to air temps. Your walls are 5 degrees warmer than the air if that holds your ambient could be 70-73ºF in the enclosure I know there is no relation it is just to make a point. i don't like seeing below 76º personally and prefer warmer 78º.

Yes cars are heated by radiant heat and then the convection heats the interior this is a product of thermal mass however the mass of your enclosure is relatively slight compared. I am not saying there is no difference just not much.

So you would also say a UTH makes a large difference in air temps?

I am interested because I tested my 40w panel 6 ways to Sunday and I found at most 3º difference not much at all. I spend three months trying different things the largest change was adding a 12 pound rock directly under the RHP this added a handful of degrees 4 I think i don't remember but it is hardly practical or safe as it came a few inches of the panel so the snake could lodge there and cook.