i am stil not able to answer this question, however, i went a different route on identifying two points and calculating the distance then i would filter out the distances which are greater than the distance i am setting up. this is working fine, however, the only thing i am not so sure is the margin of error. it seems like it increases as i increase the distance between the two points i am testing. i also wonder if the distance calculated by the geo-spatial functions are direct distances, driving distances, etc.
anyways, i dont think this is an issue for me, however, i would still try to find out how to create the polygon from a point and a distance provided. i may have to create a custom function for that scenario.