It's an odd stock design since it takes the intake from rear while the front is the exhaust, counter productive since most of the time, heat will build up at the back of the case due to the smaller enclosure of your desk. And they didn't even bother with adding an air vent at the bottom of the PSU area since a number of power supplies now have a large 120mm fan on top so this does almost nothing to help cool that part. I've seen even smaller SFF cases that had more cooling than your case and it comes at a shock since I've used Lian Li case (my current case is) for a long time and always liked their design.
Try changing the front as the intake and the rear as the outtake and see if that helps any bit (doubt it since that front fan is basically useless). As for temps, with a 23C ambient room temp with a proper case that has airflow, you should be around the 46-50C range.
AMD says the maximum safe temperature to run any FX-series processor at is 61C
I'd say, leave your side panel open and put something like a house fan on it to see if the actual problem is the case and not any other heat issue with an improper cpu cooler.