How Noise Pollution turns $80 heatsinks into $30 heatsinks
I think this artiicle in a round about way explains why fan adapters do not work.
Take an Oversized sink like the AX7 (20 cubic inches)slow the fan down so it is at an equal noise level and it takes a performance hit of 6C on a 100 W
Now take away 25%-50% heat sink volume and you lose another 3-6C, now you are in the mediocre range of performance- It's a wash
I would bet that if you did a test of swiftech, alpha and AX7 same fan they would all come out on the .34 C/W point @ 38 dBA more or less. A different picture when you use a constant in your testing
It is legitmate to take a large sink and leverage noise reduction with the added performance capacity. Although the glaciator performed as well, but that is pure copper vs. hybrid al/cu.
It makes sense to me that a fan adapter on a smaller sink is not going to give you much, if any bang for da buck.
Just my 2 cents