a body kick landed clean on the body, does not need to move the fighter to score.... if the kick lands on the arms of the opponent and is unanswered it scores just as good..... a low kick needs to show physical movement of the fighter or physical pain in the fighters expression to score in the same sense.... a low kick for instance that took a fighter off his feet would score more imo than a clean bodykick as off balancing your opponent is the key goal.... the same with the round knee and the straight knee.... a clean shot and delivered on balance is what your looking for so if the round knee delivers better and makes the fighter feel some discomfort from it and they show it where as the straight knee just hits the target then yes the round knee will score better as it shows more affect...
hope that answers your question steve.. ;)