I have been using CPA bidding on adwords on a display campaign. I used to run two popular sizes 300x250 and 336x280 in the same adgroup. This set up has been working fine.
Now I have a requirement to increase the market share. (New responsive ads are not an option because of our brand requirements.) Hence, I have added all 20 different accepted sizes. (Reference: Kindly see non-animated image ads section in https://support.google.com/adwords/answer/1722096?hl=en)
Among the sizes, some are very small banners like 300x50 while some others are very large like 300x600. Quite obviously the bid requirement for 300x50 will not be same as that of 300x600 due to real estate.
Under the above stated circumstance, should I add all 20 sizes into the same adgroup and hope CPA will take care of individual ad level bids? Or will it be wise to separate ads based on sizes into different adgroups?