2 Mafia Sites, EXACT Settings & Keywords in Adwords, 1 Gets More Impressions/Clicks. Why?

Let me premice this by saying, I am NOT an expert. In fact, I am just learning the marketting and internet advertising end of things, so I will write in my terms. Please excuse me. I need all the help I can get.

I have an adwords account. I get 2500 a month to spend from my investor who belives in the project, for adwords ONLY. It is my job to spend it, and find a CPA of .50 cents.

I was told that the average spend for 1 sign up on the site is about 1-2 dollars. It is my job to spend the money, and find a CPA of .50 cents.

I have to say I am doing a GREAT job finding the CPA slowly. I have went from 20.00 CPA to 1-3 dollar CPA consistently, in about 3 weeks of analyzing the keywords, and what you guys would call 'optimizing'.

I found a list thats working fantastic for what we need (of course id love to see better, and reach the .50 goal), but eventually google allowed me to set my max CPA as I needed, from thier optimization tools and budget settings, and it has been going fine for 1 of my games.

My newest game hasnt gotten hardly any traction from this SAME exact list. And it's settings are the same as my other game.

Why would this be? What would play a factor?

Help anyone?