I am more of an air guy than water but I had some Idle thoughts on fluid flow/block design some & basic air stuff may be applicable maybe not.
It would seem to me that you would want to accelerate flow at the hottest point over the die- You could do this by contracting the block channels, say some thing like 2 to 1 or 3to 1. This in effect would give you 5-10 higher speed nozz3ls right at the die. probable geometry might be uniform channel walls with decreasing height and cover would have to dovetail into the channel to make up the difference. Or have "V" type Channel walls although they might be harder to construct and take more space.
Also I do not see much about augmentors or ejectors. An Augmentor can add 25-40% to your flow. Most Home well pumps are usually fitted with an ejector, industrial smoke stacks often have ejectors which add sometimes 45% to the flow. Common in jet engines and as simple as a purfume bottle with aspirating bulb. You have a primary flow you just need a way to induce the secondary flow. There are litterally thousands of examples out there.
I was also curious as to whether anybody out there has tried running compressed air through a microchannel block
I have read some papers on it and has some potential. Could be quiet run the line from the compressor from the garage or basement. Maybe get a little of that abdiatic action.
I may be way off base here but thought it might be interesting to some.