The confusing info is listed right before you begin the online app here;
https://my.uscis.gov/forms/petition-for-a-relative/start/overview
But the bit from the instructions page is pretty definitive so I’ll move on.
My income is mostly US based but I’m an artist and I travel around to perform so it only gets more complicated I’m sure. The pandemic has made living in Costa rica and traveling from here impossible to sustain and my work in Europe is now very rare. However, I don’t have any residential status in Costa Rica and have kept my permanent address in MD with family. Both kids are US citizens tho so I’m not expecting any issue there. I’m at the very beginning of this process obviously.