The small words can always be problematic. The best way to get small words understood is speaking complete phrases. When there is a mistake try correcting several words which include the mistaken word. As an afterthought, I have learned I have to train myself to speak differently very often. With one speech recognition program I use, When I say the I actually have to say thee to get the program to recognize me.
Experienced users realize it is as much a matter of training the user as training the program.