Opt-in rate of email sign up form

Recently I have added a banner on the right panel of our articles page, which includes an email text box for the user to input their email address, submit and subscribe. A link will be emailed to the user to download the ebook. However there are only as little as 9 subscribers in one month.

Questions Is this consider bad response?

How about having banners in between the articles content? Many sites are doing this.

What is the best way to consider what type of banners and placement are more effective?