If you live most of your days in Missouri, you are a Missouri resident and you need to pay Missouri state income taxes, and maybe local income taxes as well. If you/your company is paying California income tax instead, that's a problem for both of you.
And, if you live in a country that does not tax resident foreigners whose entire income is foreign, you pay no income tax at all. The only countries I know that do this cheaply are Costa Rica and Uruguay (the Bahamas have expensive requirements).
One technique is to not live anywhere more than six months but be a residency in one of those countries.
I haven't done this because I have kids and pets.. but it seems pretty awesome if you make a competitive salary (not Facebook!).
There are no bright lines in residency law in the USA. You can potentially reside in one state for five months and the other for seven but be domiciled in the former. This is an area where you really ought to rely on professional advice.
