okay- well, polyamory is a lot more than the size of a penis. It seems odd that you think of other men simply as a penis, but okay. I guess there is some fear of her finding someone she would rather be with?? Is that what is going on with you??
How would you feel if she meets a guy with a tiny penis, but he shares one of her passions (not sexual) that you don't share and they start spending time together pursuing this mutual passion?
If that makes you uncomfortable, then that could be a sign that you're asking the wrong question.....