Do not think Waterloo have updated for years
"Spreading Resistance of Circular Source on Circular Disk with Edge Cooling" is not new.
Have difficulty "getting my head round" all the edge cooling
answers.so have not used to any extent.
Same applies to the non-isoflux
conditions
I assume you have followed
Groth's thread , maybe some clues there as to "what is going on in the area just above the die at radii less than the die size"