In that case, they'll have to be some type of balance. Thinking real quick about it, what can be done is that the dmg for the lvl 5 CMS will decrease (aswell as mana use) and the lvl 1 CMS dmg will increase (aswell as mana use) but at an equal amount so both CMS will do the same amount of dmg.
Example (completely arbitrary numbers here):
Lvl 5 CMS: 50dmg + 40 mana cost
Lvl 1 CMS: 20dmg + 10 mana cost
Result: Both CMS does: 35dmg + 25 mana cost
Only problem i can see now is if the low lvl Sieg dosn't have CMS. In this case, maybe the lvl 5 CMS' dmg will be cut in half. Dunno.. quick ideas.