Erlang B formula gives no of traffic in erlang from given number of channel and blocking probability. This formula gives no of blocking(call rejected) with input of number of channel and traffic. To know the formula, you can go to teletraffic handbook website and go to chapter Erlang B formula
It is logic that when you increase the blocking the number of traffic is greater because you make constant of number of channel.
Briefly the formula like this
B(n,a)= Blocking
n= no of channel
a = traffic
In you case n is constant, the different is blocking. When Blocking is less then traffic is less and otherwise.
I hope that I can help you with my explaination