It is okay to use flattering language in your LOR to support your candidature, but you should know when to stop. Showing the admissions committee that you are a stickler for detail will do nothing to improve your LOR; on the contrary, it will make it seem generic and uninteresting. You would rather address your areas for improvement alongside your areas of strength in a courteous manner, supporting them with the examples and situations stated in the prior sections. This will make your LOR appear to be an authentic document that accurately describes your candidature.