NFFI can be calculated as income of foreigners here MINUS income of our citizens/corporations abroad. As far as I understand, it's assumed that our citizens earn income by using OUR factors of production (factors of production:enterpreneurship, capital, labor, land) abroad. Here I'm interested NOT in NFFI itself, but in it's component, namely "income of our citizens/corporations abroad".
I wonder, "What to count as OUR factor of production?". There are two intepretations:
1.It's decided by location of the factor of production. So a factory that works on territory of our country is OUR factory, no matter who owns it. (With exception for enterpreneurship and labor, these are decided by citizenship of entrepreneurs and workers, thus our enterpreneurs and workers can be employed abroad.)
2.It's decided by ownership of given factor of production. So if our citizen/corporation owns a factory located in a foreign country, then it's OUR factor of production.