[BillA]

the understanding is that the thin IHS does little to laterally spread the heat, so a reasonable die simulator could be slightly larger than a 'typical' CPU
(but never so large as an IHS)

I am still abusing my 10x10mm, and as you observed the maintenance of the 'die' area is hugely important, and quite difficult
- despite the best care I can give it, after about 40 mountings the numbers start to degrade;
with professional equipment, resurfacing takes ~2hrs (.5hr on lapping machine, 1.5hrs diamond lapping) + 3hrs teardown and setup

I used to spend days hand-lapping w/o satisfaction - inspecting with optical flats

your setup looks good, just shrink that die size

EDIT:
you doing flow rate/pressure drop measurements ?
JoeC, pH, and I have started a round-robin test series - e-mail if interested in joining
- and anyone else trying to take accurate measurements