That’s one of the basic principles of traffic engineering and the Erlang formula that we accept that it is not possible to handle all of the calls all of the time.
The GOS represents the %age of calls lost to congestion during the Busy Hour.
In theory, to design a network to handle no dropped calls would require an infinite number of circuits. Try putting progressively smaller values for the GOS for the same amount of traffic in the calculator, you’ll see the number of circuits required progressively increase.
1% (or 0.8% in some networks) is the generally accepted value, but it sounds like you want a lower value. But more circuits will cost more money.