Yeap. Air flow!
So sticking these routers (or any electronics) inside a cabinet increases the need for airflows to help with the thermals. Temperature extremes (Heat or Cold) are the enemy of most electronic components which are designed for a specific operating ranges. Also remember that while temps from the CPU or RADIO chips are within their specs, they may be close enough to cook other things nearby like capacitors, etc. In general, I cannot tell you how many circuit boards I've seen where there are clearly "hot" components mounted that may have operated OK but they were cooking the boards to the point of discoloring them and guess what eventually failed! If have your router stuck in a cabinet or closet with little ambient air or you live in climate where the temps get up there and there's little A/C, then your setup might benefit for some added air-flows from a little 4" fan. FWIW, I keep a little 4" fan on top of my modem b/c there have been so many issues reported them failing. Without the fan, it gets quite warm... My advice, if you think elevating the unit helps or adding a small fan helps, then go for it. Just remember, you will have to blow out the dust every few months and clean the fan. There's a reason manufacturers avoid fans like the plague!
As always, have fun at this and YMMV! It's nice to see some wild humor... !!