I’ve added option to change those parameters, but sadly Google made a big fail about it and it seems those settings stopped working since ICS.
Take a look at those links:
http://stackoverflow.com/questions/15660805/android-extras-about-speech-recognition-does-not-work
https://issuetracker.google.com/issues/36928328
I will send unity package on your email with version having option to change those values. Maybe you want to play with it anyway.