with fan pointed down it pulls cooler air from below.
you can try an infra red gun to find the hot spots
http://www.amazon.com/HDE-Non-Contact-Infrared-Temperature-Thermometer/dp/B002YE3FS4
Phil is pointing you twords an amazing tool I use one similar to this more often then I ever thought I would. So nice to walk in mining area and get reads around machines and see my CFM's get maximum effect. With summer heats coming (and raising some already) I use it more and more.
I'm surprised on RM series I have 2 RM1000's and they always worked fine for me no heatsinks. So not sure if made nicer then smaller ones or what. But I have had them for quite a while with good luck.
rm1000 is very good gear but it is pretty hot in one spot. I mine with it in a pc 2 r9 390's doing eth coin pulls 550 watts.
case has a lot of air flow so it is all good.
I have similar experience with Fortron 500W-750W single rail series. All of them have insufficient cooling of synchronous mos-fet rectifier, so they blow before any protection shut down the PSU. Thery also put plastic insulation sheet from one side, so overall airflow is poor. Only solution is keep load at 12V less than 80%. They have 5 year warranty so opening PSU and reworking power mos-fets and heatsink is not useful.
Sometimes I buy used PSU for about 50USD and RMA my failed. They always return full price instead of repairing my PSU.
A lot of atx simply can't do 90% or more at a 24/7/365 pace.