im not alfa driver but my 1.9 jtdm has always sat dead on the mid scale on dial, it takes a while to get there if coasting off load and in cold weather but it always gets there.
im modified and run hard frequently and even though barely see the gauge wander from mid scale.(I have a nice big front mount intercooler which also slows warming up speed but still just cruising off boost will still stay mid gauge)
I see a fair few threads like this running around 70*c and im sure most were stuck open stats?
as a guide heres a pic of the injection limiter map revs on left axis and temp in celcius on top scale(x100)
you will see that it doesn't let the car have maximum fuel injection quantity in the higher revs until around 74 deg c and hits maximum at 82 deg c then starts to tail off again between 82 deg c and 100 deg c
from this id say ideal design temp must be around 82 deg c and as you can see 70 deg c is too cold your not achieving full iq potential.
I definitely find I get crappy mpg until up to temp, im sure running cool at 70 is losing some mpg
also if you look at the internal friction losses map
you can see the friction losses fall to a minimum at around 90 deg c so I would assume from this the design ideal running temp is somewhere between 82-90 deg c