are you from an other country then the google site you are trying to rank your site for, i guess you want to rank in google.com? (example, you are from europe and trying to rank your site in the US results)
google gives different results for every country. in my experience it can result in at least a 10 position difference searching from an dutch or US connection.
if you trying to rank on google.com use something like rank checker (firefox plugin) to check rankings.. thats live data, webmaster tools is outdated info, at least a few weeks old.
also 7th isn`t that great either.. i dont know if the 19k search volume you mentioned is broad match or exact match.
exact match results can be a whole lot less then broad match results.
7th place should get you about 1% of the traffic.. and thats with a great headline/title.
thats 190 visitors a month. And with a bad title and/or a badly optimized discription it could be even less...
19k isn`t that much unless you rank top 3, or at least above the fold(what people see on their screen without scrolling down) with an grabbing title and discription.
anything else isn`t gonna cut it, unless the top 5 is unrelated and not helpfull to the user at all, but that`s very unlikely to happen nowdays.
being 7th only works for keywords with over 500k searches and if you optimize your title and discription the right way..