Do you keep the computer on 24/7? I do and one thing I found with my mini 9 was that if I had it sitting on a surface where it couldn't get good air flow underneath, and left the lid down when not in use, it would heat up a lot. I subsequently would leave it on a milk crate, that has holes in it, and left the lid open overnight or during extended non-use periods.
With my 11z I have the extended life battery, so since the battery sticks out on the bottom, the computer automatically has more space underneath it to vent. I also always leave the lid open when not in use.
If you don't have the extended life battery I'd suggest leaving the computer on a crate with holes in it, or something similar, when not in use. Also keep the lid open.