Ok so this is what I think Mercedes are doing. We heard from scarbs that they are running an air to water intercooler which matches what we've seen in the sidepods (standard rads). This means that they run extra large radiators but only need 2 with much less plumbing. If you look at these 2 pictures you can see that A the compressor exits towards the right (in gold) whilst the oil tank is packaged to the left and B they run a fuel tank that is asymetrical with more space in the left hand sidepod (to the right of the images we've seen so far).
This space is where I believe the intercooler is placed, I have drawn some arrows on this pic to show where the hot air from the compressor comes out (matches well with the engine pic) and then we can see where it goes into the engine air box.
To give a sense of scale this is the
Ferrari intercooler setup, seems round about the right size.
Let me know what you think.