Possibly because you forgot to reduce the R factor. If you infect people over 1/2 the time, perhaps you need R to be 1/2 what it was before. I assume that the

Possibly because you forgot to reduce the R factor. If you infect people over 1/2 the time, perhaps you need R to be 1/2 what it was before. I assume that the model is spreading the people you infect across the time you are infectious.