Set Admob eCPM floor value

I want to set a floor value for my Admob ads and do not want Admob to return any ads if the estimated cpm is less than the floor value. I tried doing something like

But interestingly, my fill rate is still 100%.

The impression RPM is still close to 0.5%. So either admob is not returning ads based on the floor value correctly or there’s something wrong with my settings.

Anyone know what I might be doing wrong?