I wonder why the directions always tell you to do:
<--exhaust fan |heatsink| <---heatsink fan
instead of what I have mentioned, if my way works better?
<--exhaust fan <--Heatsinkfan |heatsink|
This is ok too.
When you pull, you suck in some of the air from the sides of the heat sink. With push all of the air comes in from the fan intake and straight through the cooler.
It is not a big enough difference to worry about, and may well be the arrangement of choice if you have tall heat spreaders that need to be cleared.