Got a question...

Suppose:

->You are running a single electric 16" fan.
->The fan does not cover the radiator surface (31x19).
->There is simply not enough room for a shroud.
->The fans is configured as a puller

Is there an optimum mounting position for the fan on the radiator? As in, biased towards the inlet side or the outlet side. My gut feeling is biased toward the inlet to try to knock down the temp early, but that may not be the case. (the old melting ice quicker with cold water trick comes to mind)

Any ideas with any thermal dynamic info to back it up?

I ended up with two 16" electric (one puller, one pusher) fans on opposite sides of the core and offset to either side of the core. I initially had one 16" 2300cfm puller offset to the driver side to clear the front pulley. The single fan was not quite enough in 90+ degree summer heat sitting in traffic. After adding the 2nd 16" pusher the problem was getting the motor up to temp due to over cooling. The rad is a dual 1" core aluminum 19x24". I went with a programmable Spal controller set to kick on the 2nd fan at 205F and now no worries at all.