Here is what Consumer Reports reports has to say on repellents. In this case just as Glenn found more is better. This may be disconcerting for those with a phobia or other fear of chemicals.

http://www.consumerreports.org/insect-repellents/mosquito-repellents-that-best-protect-against-zika/

The way I read this is I along with everyone with me have not been using near enough of the active ingredients. We also have not been packing enough.