If it's being spawned off of a request, it's usually pretty sticky from my experience, but if you specify a location hint instead I've had more success with it sometimes moving to a different datacenter. Not quite sure what the spawn algorithm is because it's seemingly slightly different each time I try.
For what it's worth, when I want a DO instance near a specific point, this is pretty inefficient but I just have a worker spawn and destroy DO instances with a region hint and with slightly different names then returns the name/id of the one in the POP I want