Since there is no "official" size for rat men (or mice men in my case) I think the 10 mm should work?
Now that you ask the question, I do need to order some just to see how they compare size-wise to Reaper's 28 mm (+/-) trio and Eureka's Fantasy Mice.
Mostly depends on how you envision the size of them versus the other aliens and "Standard Issue Humans."
Gracias,
Glenn