Gradual Reduction in MF Effectiveness

[Jeger]

We're discussing whether or not MF decreases in effectiveness over time.

Actually, I believe we are discussing whether the treasure you get from repeated runs declines over time. If it does, one explanation would be that your MF declines, but there exist many others.

If we are strictly restricting ourselves to whether the MF declines over time, then it is true - you can count HDMI (high-durability magic items) as uniques. However, if we are discussing whether the treasure you get from repeated runs declines over time, then you can not count HDMI as uniques, because they are not. There exist many explanations (bad RNG is only one) why the ratio of HDMI to uniques could vary with time.