You can set up different floor prices or target CPMs for varying inventory sizes through unified pricing rules. With multi-size pricing,there is easy optimization of yield in the Open Auction as and when there are valid bids for different sizes.
Pricing guidelines for Multi-size-
Multi size pricing works with the standard set of supported sizes. Even though it supports interstitials, it does not support generation of creative for dynamic allocations with interstitial.
You can enable multi size pricing for your inventory whenever it becomes possible.
It is supported by a majority of buyers, and for the ones who do not support it, multiple sizes do not get passed along in requests. So you can ask buyers if they are supportive of it or not.
It is advisable to set only one floor price for a given size and if there are multiple floor prices for one size, the highest one if applicable.
When creating a preferred deal, you can choose inventory size as a targeting option. The bid gets filtered if the inventory that is in the deal is multi size and the buyer bids with a size that was not negotiated. On Deal Check, you can see bid responses that were filtered and what were the reasons for the same.
Opt-in,blocking and ad style rules-
With Opt-in, blocking and ad style rules, multi size pricing works differently-
For Opt-in and blocking rules, Ad Exchange matches all rules that match for any of the sizes and make them applicable for all sizes.
For Ad Style, the highest priority rule that matches any of the sizes is considered and applied to all sizes.
Order of sizes in bid request-
In case there a number of sizes-
The screen size always comes first for interstitial.
Sizes are ordered approximately on the basis of size and is most likely going to interest the buyer on the basis of their bidding history.
Set up Ad Exchange line items-
With your Ad Exchange line items, you make the sizes you want to set different floor prices available to the Open Auction. These line items must have creatives with a number of sizes.Decide what the pricing for each inventory must be, specified with size in your Ad Exchange line items via Unified pricing rules.
However, you should not add extra creatives in line items. Ad Manager rotates creatives in line items evenly by default, and one of them gets selected for dynamic allocation.