Let's call it "twin inpingement", in reference to two jets side-by-side, and leave "double inpingement" to describe what's in Cascade!
Interesting.
So instead of having a perfectly round dimple, we used an "oblong" shape, and use two jets instead of one, there might be a slight performance improvement? Got a link to this research?
The problem, I believe, is that it would significantly reduce the amount of fins (aka dimple walls), which are really critical in increasing the surface area of the baseplate. I guess it could be compensated a little bit, with a bit more dimple seperation. A flat plate isn't going to cut it, IMO.
Of course this assumes that the second inpingement in Cascade has a significant impact. A CFD model of the effect would be most interesting, at least to help visualize it.
Otherwise, the jet tubes, as I've already mentionned, are a critical part in allowing the coolant to exit. How it interferes with the jet I can only guess: a toroid "vortex"? Too small. I'd try tracing the flow paths in an experiment on a (much) larger scale, but I'm not versed enough in fluid dynamics to affirm that the larger scale would be, in any way related to the small sizes involved here. I'm also pretty sure that I'm never going to have the scaled pumping capability
