NPCs composing that spawngroup :

a_skeletal_excavator (100%)

NPCs spawning around that spawngroup :
(Max range : 100)

befallen_a_giant_rat15, range=33 (-70,-123,6)

befallen_a_plague_rat20, range=87 (-139,-25,5)

a_giant_rat (50%)
a_plague_rat (50%)

befallen_448174, range=47 (-76,-44,3)

befallen_448313, range=89 (-170,-101,-9)