The different levels of position of the joined hands shows different degrees of respect. The higher the joined hands are held in relation to the face is an indication or more respect or reverence. The wai is also used to say '' sorry '' or '' thank you ''.
For Thai people the gestures are complex but foreigners are not expected to understand this aspect of Thai culture in detail. But for those who do try to understand and participate correctly then you start to be more integrated into Thai society and culture.