Different tire companies have different size circumferences than other brand tires even if the "size" is the same. On AWD Subies the acceptable tolerence is no more than 1/4" difference in the circumference of the tire. You have to measure a mounted tire around the center of the tread with a flexable tape measure to get a proper measurement. Compare all 4 tires, if they are all within that 1/4" then you are good.

The tolerence is pretty thin, that's why rotations are so important to keep the tires wearing evenly. The easiest way to ensure the tires are the same circumference is to replace them all at the same time with the same brand/size/style.

I've seen mis-matched tires damage a center diff in only 5,000 miles...