A very interesting thought, Roger, about which I have a few questions below.
Ok, the Freightliner considerations at that time resulted in findings about the air flow, which I only transferred hypothetically to the current situation with the aluminium cooler. Up to now no one has realized the idea with the underbody plate to see what it does.
But for me it sounds reasonable even if I have only one clue for it, namely the noticeably better air supply of the air filter, which is placed directly behind the radiator.
Now if we leave (for a moment or may be longer) the ideas of the changed air flow and concentrate only on the thermostat idea.
Sorry if my questions let clearly see that I‘m just a curious layman.
Heinz please we are all layman here debating and sharing our thoughts and experiences. These are just my observations and it could all be wrong 
If that's true as you write, Roger, then with one and the same radiator in winter, the average temperature of the engine would also have to rise?
Yes. I have had my bigger aluminium rad in for a few seasons now and yes the car runs hotter in the winter. The fan runs much more in the winter and guess what, the stat stays closed with the fan running. Perversely the fan can run with the stat shut when the stat is on the cool side of the engine (it’s an easy check because you can feel the temp of the bottom hose whilst the fan is running). In the summer at 30C the fan doesn’t run much at all but the stat will often be open. Could a larger radiator (one which works effectively and delivers cooler water at its output) damage the engine because the engine has to run too warm for too long due to the compensation heat of the by-pass hose?
Yes I think possibly so. I suspect Ford match the rads quite carefully.And is there a danger of too much resulting total heat when the thermostat is mounted on the bottom at the cold water inlet side? I wonder if at some point the bypass temperature must be reacted to by a wider opening of the cold part of the mix.
Yes. I have done 2 to things to reduce my engine temp in an attempt to restore the balance since fitting the bigger rad. I’ve replaced the standard 90C stat with a Burton Power 82C stat. Also I’ve de-tuned my rad by putting a plate in front to reduce the surface area (pic below). I’m very happy with my engine temp in both summer and winter now. It happily stays mostly between 94 to 100C. I regularly check it with a scan tool.In a Ford service manual I once saw that the thermostat is electrically controlled on some models and, as Richard says, directly controlled by the ECU.
But I know that with the 4/4 the thermostat is purely mechanical. Therefore perhaps all works slower?
On the first 1.8/2.0 early Duratec the stat housing had an ecu controlled heater embedded. I believe it was needed because there is a huge lag or disconnect between the head temp under load and stat opening at the bottom of the engine. To open the stat quicker the ecu would monitor the head temp and open the stat when necessary.
I assume this did not work very well as Ford dropped it on the Duratec around 2004. They did away with the heater and went back to pure mechanical and also changed the stat from a 98C to the 90C that we see in all the Duratec Morgans. The Duratec/Morgan ECU’s still have the pinouts for the heater but it is not used. I have seen when a Thermostat on a 4/4 had to be replaced that it has a 82 degrees C temperatur mark on it. Being located at the cool side of the engine that would plausibly mean that the engine is intended to run a bit hotter than this „starting“ temperature, I would guess around 88 to 90 degrees C as I read the temperature on an OBD but I will recheck this readings.
Yes. When the stat is on the cold side the stat ‘cracking’ temp is not the same as the engine or cylinder head temp. 
