Well, my Yamaha RX-V659 receiver has (approx) 4 feet above it, 2 feet on one side, and about 9 feet on the other. There are advantages of having it on top of the rack!
3 inches is probably ok, with the sides and back open, there should be enough airflow around it. Was the 111 degrees measured when it was idling, or was during or right after you played a movie at high level? You got me curious, and I took my temp gun out, and my 659 runs about 86 at idle, and about 120 at pain level. That's just pointing it at the top of the grill in the top rear. It jumps around quite a bit. Basically, if you can touch it as long as you want to, it's ok. If it's touchable, but only for a few seconds, it's borderline. And if it sizzles, well, that's too hot!
You can always put a couple of those little fans in the shelves to blow air around, if you get good ones, and don't run them full speed, they are very quiet. I've had to do this a few times due to cramped shelves. One decent sized one is usually enough. I had one on each side of the receiver I used for my PC audio playback, one pulled air in from the left, and the right one pushed it out. Dropped the temp almost 40 degrees. Even then, it wasn't pleasant touching the heat sinks if you had it turned up. It lasted for almost 20 years, so I guess it was ok. Main filter caps shorted and exploded one day, and it smoked the PC board to the point it wasn't worth fixing.