I've found that as well. I wondered if it didn't have to do with them being more jumpy and having a stronger odor with more fur?
Something I've tried this year with bigger hatchlings (75-100g) is rat crawlers/pups (something with lots of fur that's fairly mobile). And that's worked out really well in terms of taking a rat first try.
I actually haven't had to use mice at all yet this year *crosses fingers*