Kept AdSense but added a price floor and it stopped underselling

Kept AdSense but added a price floor and it stopped underselling
Ok so AdSense was filling my top unit at $1.80 CPM when the inventory was clearly worth more. Set a floor through the ad manager so AdSense had to bid above it or pass.
— Floor set at $3.00 on the above-fold unit
— Fill rate dropped to 88%, who cares
— RPM on that slot $1.80 → $3.40, total page RPM +19%
A passed impression beats a dirt-cheap fill. Floors force the auction to respect your inventory. Test it on one page first.