Not sure this is the best place to post but hopefully someone can shine some light on this: Recently set up a new FB campaign to a pretty targeted group on a Conversion basis (estimated £30-£60 per conversion) and bid at around £40. This worked pretty damn well and was seeing 3%+ CTR for about 5 days with around 50-100 clicks a day. After this validation period I wanted to try and lower my costs. The average CPM during this was working out to around £6.50 which seemed unreasonably high, so I switched over to CPM basis (estimated £0.80 - £1.20) set Max Bid at around £1.30 - the ad remained unchanged in every other way. However, since switching to CPM I'm only reaching about 20% of original reach and CTR has plummeted down to <1%. I'm positive this is not due to ad fatigue as this happened exactly after the switch. I would have expected a gradual lowering of CTR if it was just down to ad fatigue. So, I've read come have claimed that FB reserves inventory in their favour - i.e. the CPM traffic I'm getting is their worst. Have any of you experienced this, and any tips on how to work around it?