Kudos for using a polar map. The more I learn about polar map charts, the more useful I think they actually are. Here is a informative presentation by Earl Geddes on the matter, who is, as far as I know, the chief proponent of Polar Maps as a measurement of loudspeakers, he gets into polar charts at around 13:00, but you will want to watch it from the beginning for context:
[video=youtube;fE2nWVwFT9k]https://www.youtube.com/watch?v=fE2nWVwFT9k&feature=youtu.be[/video]