Ok, never mind. I just shot my 28 2.8 manual on each full stop at the same scene. You are correct. With 'evaluative' metering the exposure seems to vary a LOT. It is much better with 'partial' metering, but it is still variable.
Metering pattern does not matter. For example, the sample which I posted earlier was with a meter in Spot mode. Metering automation (Av, Tv, M) also does not matter.