Here is a pic of my BIX:
That is only 1" tall because that was as large as I could make it and get it to fit.
Here's my current rad:
http://www.procooling.com/~phaestus/becoolingrad.jpg
2" clearance between the fins and the fans.
I highly recommend reading this article:
http://www.nmbtc.com/pdf/forum/engineering_101.pdf
Page 3 has P-Q curves for fans with restrictions at different lengths from the fan on either the intake or exhaust side. This is the "why" for using a shroud rather than strapping fans right onto radiators.