When a State effect is recast on someone with a state effect the level is increased but not doubled. The increase works as follows...
Half the level (round down) is added to the existing effect.
i.e. Evangaline casts Holy Armour on Kronnen giving him a bonus to his armour, the effect is level 2 Shield. after the following maintenance phase Evangaline again casts Holy Armour on Kronnen.
Kronnens Shield has been reduced to level 1 because of the new round, the spell from Evangaline normally gives Shield level 2 but as Kronnen is already under the spells effect the level of Evangalines second holy armour is halved (rounding down) for only a single extra levels power restoring Kronnens Holy Armouor effect back to level 2
If Evangaline had a Level 3 Shield to cast in the round after the initial cast the rebuff would still only add +1 level as +1.5 is rounded down.