Different coolant temp readings

Car: Audi TT Mk 1 (2001 model), 225 quattro convertible.

I was using a value from the engine controller for my coolant temperature.  I changed to a value from the Instruments controller so I could have it on the same screen as oil temperature and ambient.  However, it reads a slightly different temperature - 2 or 3 degrees higher than the other one.  I haven't tracked it down precisely, but I think the first one is taken from the radiator OUTLET, the second from the radiator INLET (ie before the coolant has been through the radiator).

You can't have both on the same screen but it looks as if this is a way to check on the efficiency of the radiator.  Does that sound likely?  A difference of only 3 degrees?