I never understoo that but… is leveling cumulative? If I have a munition that increase 3% hitpoints in level 2 and 4% in level 5… it will increase:
100 to 103 in level 2
100 to 104 in level 5 (substituting earlier levels)
Or
100 to 103 in level 2
103 to 107 in level 5 (cumulative to earlier...