Glad you were able to resolve this. Terragen is pretty robust/flexible and allows values outside of the slider range to be typed into almost any input field. Sometimes this is very useful, sometimes the results are just crazy.
Generally the slider range tries to represent a good or reasonable range of values, but feel free to try outside of those values (except I would generally not recommend doing so on e.g. the detail/quality sliders in most cases).
- Oshyan