pusher vs puller fan

[sd88supra]

ok, i got a flex-a-lite 16" shrouded 2000 cfm fan... it still overheats, but very gradually. the temp gauge doesnt go up until ive been idling for several minutes. works fine for normal driving, even at traffic lights, but its gonna still be overheating under very heavy traffic. and im still getting that coolant boiling. it even looks like it sucked my reservoir bottle (it was almost collapsed) though the reservoir was full.

ive mounted it behind the radiator, as a puller. i didnt have to reverse the blades because it came puller ready, i just had to wire it as a puller.

-2000 cfm
-16" diameter
- shrouded
- puller

what i was thinking though, is that since the fan clutch is farther away from the radiator (and my electric fan is attached to the radiator) it could have something to do with it not having enough room to pull air from. any ideas/suggestions?