White lip Genders?

[Kreamcheese]

So my little guy is the only one that I hear croak. I have never seen my larger frog croak. Also the size difference is at least an inch between them, so is it safe to assume I have a female and a male?
I do realize these frogs don't or are very difficult to breed and I don't plan to try but It would be cool to have one of each nonetheless.

[John]

I think the chances are good that the bigger one is female.