There's lots of info about building 13% exact match anchors, but how does google know which are main keywords that you are trying to rank for. Is it that google just ranks higher that 13%. If you have 13 keywords and they make up only 13% of your total backlink profile, why does google rank for these? Is it better to have just 3 keywords that you rank for which have 4 % each which totals close to 13% etc? What is the optimum amount of keywords you should rank a page for? 1 keyword, 3 etc?