I have a large Greek army. The majority are AB, but I have a few Xyston mixed in. The Xyston figures are slightly smaller but the size of the shields are
notably smaller and in a wall of shields it looks a bit odd if you mix them. It also doesn't help that some of the AB are closer to 20mm.
I mainly used Xyston in separate units and for command bases.
This pic have Xyston peltasts in front of some AB hoplites.