What these studies actually show is that a frontier in this sense is more of a relationship or conflict between civilizations. Scenarios where one single group was moving unimpeded into unoccupied land are very rare (only once per region ever!) and mostly unattested in written historical record so there simply isn't much to say about the actions or attitudes of the individuals within them.

Basically almost always your frontier is also their frontier, the people you are trying to replace. You aren't acting on your own, for example in the US the western expansion depended heavily on connection to sophisticated trade networks, financial technology, and straightforward military support. Individual action is only one small part of what makes this process work, but is the part most highlighted after the fact by the winning side.