Which site are you talking about? The web hosting site or the web directory? I don't think website topic affects CTR. It affects your cost per click. Your CTR depends on other things such as ad placement, ad format and relevancy of the ads.
placement and size might affect your CTR but topic never. However, the content of your site can affect your CTR. This is because the visitor will like to know more and click on the ads if your content is interesting enough
Well obviously you'll need to increase your traffic before even worrying about placements and stuffs.