What is the role of Rate in an Admob house ad campaign

Question

I have made a campaign before in the distant past but this time google has updated the design/functionality and now I have to tell a Rate even in a house ad campaign. I have set the target to 80% of total impressions, so I think my ad should be shown 80% of the time regardless of the rates of third parties. I think I am missing something here. Please have a look at the screenshot and tell me what should I put in the Rate input box.

Basically I have made/trying to make a campaign which shows ad of another app of mine in the specified app using my personal inventory and ignoring third party ads.