Interesting. I acquired my 36 a couple of months ago. On my first trip to the range I started by firing some 148gr. wadcutters, just to get a feel for the gun. Everything I shot was consistently high of POA. Midway through the session I switched to some 130 gr. FMJs that I happened to have in the range bag. They shot right to point of aim. Since then, I've been using lighter .38s (120-130gr. rounds) in the gun with great success.
I've wondered whether it's me or the gun. To be honest that front sight is awfully hard to visualize on the 36 and it may be that I'm actually aiming the gun consistently higher than I think I am. Thus, my TRUE POA may be somewhat higher than I think it is. Lighter bullets, as a rule, tend to hit lower than heavier rounds, and perhaps the lighter rounds are simply compensating for my aiming error.