@TheForgotten20 this is ez to solve, instead of making a 1x1 kill zone, make it 1*x, e.g. 1*5 .. this gives them walking room and from object collision they will automatically spread out

Mobs also tend to bunch up in the corners, so a 2x2 will actually fit more than a 1x4. a 2x2 should also be plenty for 100 mobs (i.e. server limit) so there's no need to go any bigger.