It's best to complete battle square at chapter 4. I completed battle square in chapter 2 and I always reloaded 'til I get xp award. I gained lots of level but the xp I gain in chapter 3 & 4 was reduced because my level was high. Wish I had completed battle square when I was chapter 4. My party could be 1-2 level higher with that way
Whatever, here's how I played battle square. I cast buff spells to my fighter. Then he attacks. I reload when air elemental appears. Shadow creatures easy.