I have found the farther away you are from your start island the more likely a higher star boar is to spawn. If you have a meadows base look for a boar stone as far from the center of your start island as possible. The first 2, 2 star boars I found were on an island 4 islands away from my start spot not near a boar stone or an abandoned farm but right on the edge of the plains.

I still haven't found a 2 star boar on my start island only a 1 star and it was on the east coast of the start island. That coast was 3 times the distance from the start stones that the west coast was away from the start stones.