Two components will look as good as four, unless you put them in direct competition with human hands. We're working toward improving the blends for attracting yellowfever mosquitoes and adjusting the blends to attract other mosquito species. Finding a blend and testing it isn't all that has to be done. Many things could affect why a blend is attractive or not. We test to see if the location or position of the cages affects the results.
Time of day is also extremely important.
Entomologist Daniel L. Kline tested the attractiveness of socks worn by humans. I wore the socks for 12 hours on 3 consecutive days. I also found mosquitoes love Limburger cheese. Incidentally, Limburger cheese was first made in The Netherlands by monks. They trampled the cheese with their feet to get the finished product.