Honestly, every time you try and hold FB to a set of rules - it breaks them. Some creatives just take off and do better in the beginning which can determine the rest of their lifespan. Find a solid creative that sticks above a .10-.15 CTR and give that the majority of your budget's attention. Ad history helps to determine your CPM when you're bidding CPC. CPM bidding is cool, but usually not in the UK unless your CTR is above a steady .2 - .3ish.
Hope this helps.
Hope this helps.