How is GC distribution used exactly

hi,

I have a very simple question: PCR amplification is simulated with rounds of amplification which involve binomial sampling and an associated probability p in [0,1].

I'm interested in using the GC distribution, but how exactly is the density related to the amplification efficiency?

For example phi(0.5; mean=0.5, SD=0.1) = 3.989423 > 1 which cannot be a probability.

Is the density cropped at 1? Scaled such that max(phi) = 1?