So far I've discovered that it matters but it's not important.
Always towards the back.
Whether you push or pull can make a 2 degree difference according to some nerds.
Another person had the same RAM clearance issue and put the fan on the incorrect side and pulled throught the synch. He had no trouble for years.
The sides of my cooler are not the same, suggesting that it was done deliberately for some advantage but If I have the fan on the incorrect side I will have to turn the cooler 180 degrees because there are two rubber strips that make a better seat for the fan and they're only on one side.
I'm leaning towards 'who cares' because it shouldn't make a difference whether you push or pull. Anyone?
For that cooler, it should not make a significant difference for cooling the CPU. It could affect the inside the case temperature if the hot air is blown away from the case vents or case exhaust fan(s). The rubber mounting strips can probably be removed and reinstalled on the other side of the heat sink.