The short answer is that you can't. The way it works is that you set a keyword and various advertisements are shown. The advertisements are based on your keyword, and that, along with the name of your domain. We have no control over what ads are displayed. One ad on the page may have been for $1.75, while another ad on the same page may have been for $.02. It almost seems to take a little luck, that they click on the expensive domain.
That being said, i you got a click for $1.75, that means that this domain and keyword have a high earnings potential per click. I would keep it the same, since you probably will get more expensive clicks. For some keyword/domain combinations the ads seem to range from $.00-$.05, so this keyword is probably good.