It's like the chicken and the egg. You got to start somewhere. Use whatever numbers you want to start and just see how it plays out. Another example based on what you said.

100 bucks, 300 does, 50% bucks are killed and 20% does are killed. So after hunting season you have 50 bucks and 240 does. Let's say half of the 240 does left are yearlings and have one fawn, and the other 120 adult does have twins. So now you have 50 bucks, 240 does, and 360 fawns. 50% of the fawns will be bucks and 50% will be does. So now we have 230 bucks and 420 does. That is a 1 to 1.82 buck to doe ratio.

The main point is that bucks being born every year at a rate pretty much equal with does so it is difficult to get a really high buck to doe ratio unless non-typical factors exist.