Distribution What should I set for AdMob eCPM floor for iOS and Android?

I'm setting up AdMob and it allows me to set an eCPM floor. I have absolutely no idea what number to put here and am not having much luck googling around.

I feel like if I don't set any floor then I'll get really lousy looking ads, if that makes sense. If my game has to have ads, at least let them be nice ads, you know?

All I found on the forum was this post by @sman saying that his eCPM is $3 for iOS and $.5 for Android. I don't know if this means I won't get fills with a number higher than $.5...