A Contorted Epitome's Ward Save is increased by +1 for every point of Strength above 3 that every Attack targeting it has. So, against a Strength 4 Attack it has Ward Save (4+), against Strength 5 it has Ward Save (3+) and so on.
Source: Warhammer Armies Project: Unofficial 9th Edition (v2.2)
A Contorted Epitome's Ward Save is increased by +1 for every point of Strength above 3 that every Attack targeting it has. So, against a Strength 4 Attack it has Ward Save (4+), against Strength 5 it has Ward Save (3+) and so on.