I still have to insist;
Most of the blowers air will escape the easiest path out of the heatsink. (see pic at page 1 of topic, drawn as thick lines representing more air)
It's just like water, just like electricity, where the resistance is the smallest, thats where you'll find the highest flow.
For freakin' sake, take two straws of different diameters or lenght, blow into them, now tell me, where does it flow the most???
So, if you stick a blower(radial fan) ontop of a swiftech porcupine heatsink, you'll get most of the air escaping really close to the sides, just as "normal" axial fan would push the air.
The air doesn't want to force itself down to the bottom of the heatsink and then veer off 90 degrees and take an even longer route out of the heatsink.
Ofcoz, some miniscule amount of air will reach down there "in the venerable dead spot", but most of it will be trapped in vortices(as in vortex, I hope). My "?" in the picture posted above by me is where those vortices rule. We all think/know that vortices are good for heat exchange, but these ones are trapped, and not much air is rushing by to the rescue.
In my picture you can see thick lines representing where more air pass by... the thinner lines, the less air I predict will pass by...
Yes, the cooling of the dead spot IS BETTER with a blower, but so far as for practical solutions go, it has been a too high trade-off in CFM to make the idea work in practise.
Oh yes, radial fans has a potential to create better pressure, but that needs either high rpms(we know how that sounds) or bigger diameter paddle wheels(we all know already the devices are clumsy "as is").
Another factor speaking FOR AXIAL fans is the air coming of the blades is turbulent, and that turbulent air hits the fins/pins and then escapes the easy way to the sides.
The air from the radial fan is much less turbulent, of coz it might GET turbulent passing the fins/pins... but from the get-go the axial air is more turbulent.
