I have been trying to figure out where to put my conventional 10x30x5 cm Setrab oil-cooler for the Rotrex unit and avoid having to stack 3 coolers (oil, IC, coolant) in the grille opening.
Both my fog-light openings in my bumper  are already occupied for the engine oil-cooler and CAI.

I have heard of water to air intercoolers but did not know there were water to oil coolers available for automotive use before reading about laminova coolers from www.laminova.se :

This looked like a major win: No airflow needed, the amount of oil from rotrex will not tax water cooling much, clean install etc.
After ditching AC I have enough space ato add a ~ 20 cm long C43 Laminova unit in the hose going from rad to engine block. Problem solved ?

The Rotrex inlet oil temperature should be max 80 C which is quite cold when dealing with petrol engines where optimal coolant/oil temp are around 90-100 C.  My oil and coolant temps can reach as high as 120/105 C on track days.
According to testing done by Flyin Miata the temperature drop for a radiator in a Miata is only around 5 C when inlet coolant temp is 105 C  -->  http://www.flyinmiata.com/tech/rads.php

radiatorAmbient tempRad inletRad outletImprovement over stockTemperature dropTime to tempOutlet temp compared to ambient
stock 1990-9735º105º100º -+65º
Brand X aluminum race radiator38º105º101º+1º15:44+63º
FM crossflow43º102º98º-2º17:09+55º
dual pass44º102º97º-3º11:55+53º

That means a laminova cooler would  act as a heater instead of cooler if used with the Rotrex.

But what about using it as regular oil-cooler for the engine and use my current engine cooler for the Rotrex ?
Here are some graphs from laminova.se for the C43 with 120 c oil inlet temp and 85 c coolant temp:
 I have not found any coolant or oil flow numbers for the Miata but this  site says an oil pump typically delivers between 8-12 gpm or 30-40 litres/min
As for coolant flow I don't have a clue.  I found an example here where a 20 gpm water pump actually delivers 0 gpm at 6psi pressure drop.  Lets just say the miata pump can deliver 160 litres/min to make it near optimal for a laminova cooler with a bypass.
A C43-182 would then cool my 120c oil down to 116  given my coolant inlet temp was 85C.
However my coolant temps are most likely 100+ C  which I'm afraid would make this cooler useless as anything other than an oil heater.