You are not supposed to play 5* maps anyway.
There is no "best" area, the higher the area the better your aim will become, though. More room to work with, better developing of muscle memory plus higher presicion. If you change your tablet area every second day you will develop no muscle memory at all, so pick something that is comfortable to you and stick to it. Some pro players like Totori change it occasionally, I don't know if that is a smart move, but they probably know what they are doing.
There is no "best" area, the higher the area the better your aim will become, though. More room to work with, better developing of muscle memory plus higher presicion. If you change your tablet area every second day you will develop no muscle memory at all, so pick something that is comfortable to you and stick to it. Some pro players like Totori change it occasionally, I don't know if that is a smart move, but they probably know what they are doing.