RAX45 Upside down mount?

I've mounted my new router AZ4300 Nighthawk Model RAX45 on the ceiling of a room near the center of my house. See below attached file for a picture. The unit is attached using the built-in mounting arrangement on the bottom, and is quite secure.

My question is this. Reversing the mounting this way will reverse the air flow through the unit. This may be the opposite of the way it is designed for, possibly resulting in higher internal temperatures. OTOH, this orientation may have been just another consideration in the original design.

Taking the temperature with an IR thermometer through the vent grid on the top just in front of the antennas shows a 9° C rise from my current ambient of 30° C. 

Are there any issues with mounting upside down in this way? It would seem to me that the ambient temperature should be well within the rated temperature of the design, which the manual says is up to 40° C ambient. So, the only way I should ever run into trouble would be if the ambient actually got up to 40° C.

Just thought it might be a good idea to check since there seems to be a lot of contradictory advise when I google search on the topic.

Thanks for any thoughts.