Yeah, all my fans are placed atop the AVRs to pull air up.
This works extremely well. My AVRs are always cool with dual AC Infinity 120mm fans atop.
The ventilation holes are on top of the AVR, not in the rear.
These are the fans I use. They cost $20 for 2 x 120 mm fans.
https://www.amazon.com/AC-Infinity-MULTIFAN-Receiver-Playstation/dp/B00JLV4BWC/ref=sr_1_2?ie=UTF8&qid=1520452870&sr=8-2&keywords=AC+Infinity+120mm
You need to find a place that allows at least 2" above the AVR.
What is your setup look like? TV stand? Audio Rack? Cabinets?