24-48 w/ 3 day and 6 day vacay question.

Hey Guys, 

 My department has run into a few problems lately with how the brass is treating us. We have a question that maybe some of you can shed light on. 

 We work a 48 hour week schedule and don't get paid overtime for any hours until they hit 53 hrs +, which is what FLSA labor laws state, but to my understanding the labor law says that that applys to firefighters who work a 24-48 shift schedule where there is a short pay period and a long pay period (small check / big check ) . However our schedule is not based on that and we are not getting paid for the hours that we aren't scheduled to work as overtime. In other words we work the 48 hours but have to stay over 12 hours and we only get 7 hours overtime pay instead of the full 12 hours which is what would be morally correct. Our chief says that he can do that per Federal labor laws, but we don't work the 212 hr shift schedule or whatever you call it. We were hired on a 48 hour work week. The schedule rotates around a 6 week rotations where every 6 weeks we get a 6 day vacation to prevent us from getting mandatory overtime pay.  I attached a two month schedule to give you an idea of what I am talking about. Any help would be appreciated